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LTC2983 Datasheet by Analog Devices Inc.
LTLII‘IM
TECHNOLOGY
W
W
H
L7 LJUW 1
LTC2983
1
2983fc
For more information www.linear.com/LTC2983
TYPICAL APPLICATION
FEATURES DESCRIPTION
Multi-Sensor High Accuracy
Digital Temperature
Measurement System
The LTC
®
2983 measures a wide variety of temperature
sensors and digitally outputs the result, in °C or °F, with
0.1°C accuracy and 0.001°C resolution. The LTC2983 can
measure the temperature of virtually all standard (type B,
E, J, K, N, S, R, T) or custom thermocouples, automatically
compensate for cold junction temperatures and linearize
the results. The device can also measure temperature with
standard 2-, 3- or 4-wire RTDs, thermistors and diodes. It
has 20 reconfigurable analog inputs enabling many sen-
sor connections and configuration options. The LTC2983
includes excitation current sources and fault detection
circuitry appropriate for each type of temperature sensor.
The LTC2983 allows direct interfacing to ground referenced
sensors without the need for level shifters, negative supply
voltages, or external amplifiers. All signals are buffered and
simultaneously digitized with three high accuracy, 24-bit ∆∑
ADCs, driven by an internal 15ppm/°C (maximum) reference.
Thermocouple Measurement with Automatic Cold Junction Compensation
Typical Temperature Error Contribution
APPLICATIONS
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Patents Pending
n Directly Digitize RTDs, Thermocouples, Thermistors
and Diodes
n Single 2.85V to 5.25V Supply
n Results Reported in °C or °F
n 20 Flexible Inputs Allow Interchanging Sensors
n Automatic Thermocouple Cold Junction Compensation
n Built-In Standard and User-Programmable Coefficients
for Thermocouples, RTDs and Thermistors
n Configurable 2-, 3- or 4-Wire RTD Configurations
n Measures Negative Thermocouple Voltages
n Automatic Burn Out, Short-Circuit and Fault Detection
n Buffered Inputs Allow External Protection
n Simultaneous 50Hz/60Hz Rejection
n Includes 15ppm/°C (Max) Reference (I-Grade)
n Direct Thermocouple Measurements
n Direct RTD Measurements
n Direct Thermistor Measurements
n Custom Sensor Applications
2983 TA01a
°C/°F
VREF (10ppm/°C)
LTC2983
24-BIT
∆∑ ADC
24-BIT
∆∑ ADC
24-BIT
∆∑ ADC
RSENSE
2k
1
4
2
3
0.1µF
2.85V TO 5.25V
1k
1k
PT-100
RTD
LINEARIZATION/
FAULT DETECTION SPI
INTERFACE
TEMPERATURE (°C)
–200
–0.5
ERROR (°C)
0.3
0.2
0.1
–0.1
–0.2
–0.3
–0.4
0.5
200 600 800
2983 TA01b
0
0.4
0400 1000 14001200
THERMISTOR
THERMOCOUPLE
RTD
3904 DIODE
LTC2983
2 L7LJ1‘JW
LTC2983
2
2983fc
For more information www.linear.com/LTC2983
TABLE OF CONTENTS
Features ............................................................................................................................ 1
Applications ....................................................................................................................... 1
Typical Application ............................................................................................................... 1
Description......................................................................................................................... 1
Absolute Maximum Ratings ..................................................................................................... 3
Order Information ................................................................................................................. 3
Complete System Electrical Characteristics .................................................................................. 3
Pin Configuration ................................................................................................................. 3
ADC Electrical Characteristics .................................................................................................. 4
Reference Electrical Characteristics ........................................................................................... 4
Digital Inputs and Digital Outputs .............................................................................................. 5
Typical Performance Characteristics .......................................................................................... 6
Pin Functions ...................................................................................................................... 9
Block Diagram ....................................................................................................................10
Test Circuits ......................................................................................................................11
Timing Diagram ..................................................................................................................11
Overview ..........................................................................................................................12
Applications Information .......................................................................................................16
Thermocouple Measurements .............................................................................................................................. 21
Diode Measurements ............................................................................................................................................ 24
RTD Measurements .............................................................................................................................................. 28
Thermistor Measurements .................................................................................................................................... 43
Direct ADC Measurements .................................................................................................................................... 55
Supplemental Information ......................................................................................................55
Fault Protection and Anti-Aliasing ......................................................................................................................... 57
2- and 3-Cycle Conversion Modes ........................................................................................................................ 57
Running Conversions Consecutively on Multiple Channels ................................................................................... 58
MUX Configuration Delay ...................................................................................................................................... 58
Global Configuration Register ............................................................................................................................... 59
Custom Thermocouples ......................................................................................................... 59
Custom RTDs .....................................................................................................................62
Custom Thermistors .............................................................................................................65
Package Description ............................................................................................................70
Revision History .................................................................................................................71
Typical Application ..............................................................................................................72
Related Parts .....................................................................................................................72
LTC2983
L7 LJUW 3
LTC2983
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2983fc
For more information www.linear.com/LTC2983
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
Supply Voltage (VDD) ................................... –0.3V to 6V
Analog Input Pins (CH1 to
CH20, COM) ................................. –0.3V to (VDD + 0.3V)
Input Current (CH1 to CH20, COM) ...................... ±15mA
Digital Inputs (CS, SDI,
SCK, RESET) ................................ –0.3V to (VDD + 0.3V)
Digital Outputs (SDO, INTERRUPT) –0.3V to (VDD + 0.3V)
VREFP ........................................................ –0.3V to 2.8V
Q1, Q2, Q3, LDO, VREFOUT, VREF_BVP (Note 17)
Reference Short-Circuit Duration ..................... Indefinite
Operating Temperature Range
LTC2983C .................................................0ºC to 70ºC
LTC2983I ............................................. –40ºC to 85ºC
LTC2983H ........................................... –40ºC to 125ºC
(Notes 1, 2)
ORDER INFORMATION
LEAD FREE FINISH TRAY PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2983CLX#PBF LTC2983CLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP 0°C to 70°C
LTC2983ILX#PBF LTC2983ILX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 85°C
LTC2983HLX#PBF LTC2983HLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
13
14
15
16
17
18
19
20
21
22
23
24
48
47
46
45
44
43
42
41
40
39
38
37
VREFOUT
VREFP
GND
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH8
CH9
25
26
27
28
29
30
31
32
33
34
35
36
CH10
CH11
CH12
CH13
CH14
CH15
CH16
CH17
CH18
CH19
CH20
COM
12
11
10
9
8
7
6
5
4
3
2
1
GND
VREF_BYP
NC
GND
VDD
GND
VDD
GND
VDD
GND
VDD
GND
Q1
Q2
Q3
VDD
GND
LDO
RESET
CS
SDI
SDO
SCK
INTERRUPT
TOP VIEW
LX PACKAGE
48-LEAD (7mm × 7mm) PLASTIC LQFP
TJMAX = 150°C, θJA = 57°C/W
COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply Voltage l2.85 5.25 V
Supply Current l15 20 mA
Sleep Current l25 60 µA
Input Range All Analog Input Channels l–0.05 VDD – 0.3 V
Output Rate Two Conversion Cycle Mode (Notes 6, 9) l150 164 170 ms
Output Rate Three Conversion Cycle Mode (Notes 6, 9) l225 246 255 ms
Input Common Mode Rejection 50Hz/60Hz (Note 4) l120 dB
Input Normal Mode Rejection 60Hz (Notes 4, 7) l120 dB
The l denotes the specifications
which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
LTC2983
4 L7LJ1W
LTC2983
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2983fc
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ADC ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Resolution (No Missing Codes) –FS ≤ VIN ≤ + FSl24 Bits
Integral Nonlinearity VIN(CM) = 1.25V (Note 15) l2 30 ppm of VREF
Offset Error l0.5 2 µV
Offset Error Drift (Note 4) l10 20 nV/°C
Positive Full-Scale Error (Notes 3, 15) l100 ppm of VREF
Positive Full-Scale Drift (Notes 3, 15) l0.1 0.5 ppm of VREF/°C
Input Leakage (Note 18)
H-Grade
l
l
1
10
nA
nA
Negative Full-Scale Error (Notes 3, 15) l100 ppm of VREF
Negative Full-Scale Drift (Notes 3, 15) l0.1 0.5 ppm of VREF/°C
Input Referred Noise (Note 5)
H-Grade
l
l
0.8 1.5
2.0
µVRMS
µVRMS
Common Mode Input Range l–0.05 VDD – 0.3 V
RTD Excitation Current (Note 16) l–25 Table 30 25 %
RTD Excitation Current Matching Continuously Calibrated lError within Noise Level of ADC
Thermistor Excitation Current (Note 16) l–37.5 Table 53 37.5 %
The l denotes the specifications which apply over the full
operating temperature range, otherwise specifications are at TA = 25°C.
REFERENCE ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage VREFOUT (Note 10) 2.49 2.51 V
Output Voltage Temperature Coefficient I-Grade, H-Grade l3 15 ppm/°C
Output Voltage Temperature Coefficient C-Grade l3 20 ppm/°C
Line Regulation l10 ppm/V
Load Regulation IOUT(SOURCE) = 100µA l5 mV/mA
IOUT(SINK) = 100µA l5 mV/mA
Output Voltage Noise 0.1Hz ≤ f ≤ 10Hz 4 µVP-P
10Hz ≤ f ≤ 1kHz 4.5 µVP-P
Output Short-Circuit Current Short VREFOUT to GND 40 mA
Short VREFOUT to VDD 30 mA
Turn-On Time 0.1% Setting, CLOAD = 1µF 115 µs
Long Term Drift of Output Voltage (Note 13) 60 ppm/√khr
Hysteresis (Note 14) ∆T = 0°C to 70°C
∆T = –40°C to 85°C
30
70
ppm
ppm
The l denotes the specifications which apply over
the full operating temperature range, otherwise specifications are at TA = 25°C.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Normal Mode Rejection 50Hz (Notes 4, 8) l120 dB
Input Normal Mode Rejection 50Hz/60Hz (Notes 4, 6, 9) l75 dB
Power-On Reset Threshold 2.25 V
Analog Power-Up (Note 11) l100 ms
Digital Initialization (Note 12) l100 ms
The l denotes the specifications
which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS
LTC2983
L7 LJUW 5
LTC2983
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2983fc
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DIGITAL INPUTS AND DIGITAL OUTPUTS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
External SCK Frequency Range l0 2 MHz
External SCK LOW Period l250 ns
External SCK HIGH Period l250 ns
t1CS↓ to SDO Valid l0 200 ns
t2CS↑ to SDO Hi-Z l0 200 ns
t3CS↓ to SCK↑l100 ns
t4SCK↓ to SDO Valid l225 ns
t5SDO Hold After SCK↓l10 ns
t6SDI Setup Before SCK↑l100 ns
t7SDI HOLD After SCK↑l100 ns
High Level Input Voltage CS, SDI, SCK, RESET lVDD – 0.5 V
Low Level Input Voltage CS, SDI, SCK, RESET l0.5 V
Digital Input Current CS, SDI, SCK, RESET l–10 10 µA
Digital Input Capacitance CS, SDI, SCK, RESET 10 pF
LOW Level Output Voltage (SDO, INTERRUPT) IO = –800µA l0.4 V
High Level Output Voltage (SDO, INTERRUPT) IO = 1.6mA lVDD – 0.5 V
Hi-Z Output Leakage (SDO) l–10 10 µA
The l denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at TA = 25°C.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All voltage values are with respect to GND.
Note 3: Full scale ADC error. Measurements do not include reference error.
Note 4: Guaranteed by design, not subject to test.
Note 5: The input referred noise includes the contribution of internal
calibration operations.
Note 6: MUX configuration delay = default 1ms
Note 7: Global configuration set to 60Hz rejection.
Note 8: Global configuration set to 50Hz rejection.
Note 9: Global configuration default 50Hz/60Hz rejection.
Note 10: The exact value of VREF is stored in the LTC2983 and used
for all measurement calculations. Temperature coefficient is measured
by dividing the maximum change in output voltage by the specified
temperature range.
Note 11: Analog power-up. Command status register inaccessible during
this time.
Note 12: Digital initialization. Begins at the conclusion of Analog Power-
Up. Command status register is 0 × 80 at the beginning of digital
initialization and 0 × 40 at the conclusion.
Note 13: Long-term stability typically has a logarithmic characteristic
and therefore, changes after 1000 hours tend to be much smaller than
before that time. Total drift in the second thousand hours is normally less
than one third that of the first thousand hours with a continuing trend
toward reduced drift with time. Long-term stability will also be affected by
differential stresses between the IC and the board material created during
board assembly.
Note 14: Hysteresis in output voltage is created by package stress
that differs depending on whether the IC was previously at a higher or
lower temperature. Output voltage is always measured at 25°C, but
the IC is cycled to the hot or cold temperature limit before successive
measurements. Hysteresis measures the maximum output change for the
averages of three hot or cold temperature cycles. For instruments that
are stored at well controlled temperatures (within 20 or 30 degrees of
operational temperature), it is usually not a dominant error source. Typical
hysteresis is the worst-case of 25°C to cold to 25°C or 25°C to hot to
25°C, preconditioned by one thermal cycle.
Note 15: Differential Input Range is ±VREF/2.
Note 16: RTD and thermistor measurements are made ratiometrically. As a
result current source excitation variation does not affect absolute accuracy.
Choose an excitation current such that largest sensor or RSENSE resistance
value, when driven by the nominal excitation current, will drop 1V or less.
The extended ADC input range will accommodate variation in excitation
current and the ratiometric calculation will negate the absolute value of the
excitation current.
Note 17: Do not apply voltage or current sources to these pins. They must
be connected to capacitive loads only, otherwise permanent damage may
occur.
Note 18: Input leakage measured with VIN = –10mV and VIN = 2.5V.
LTC2983
6 L7LJ1‘JW
LTC2983
6
2983fc
For more information www.linear.com/LTC2983
Type E Thermocouple Error and
RMS Noise vs Temperature
Type B Thermocouple Error and
RMS Noise vs Temperature
RTD PT-1000 Error and RMS
Noise vs Temperature
Type R Thermocouple Error and
RMS Noise vs Temperature
Type S Thermocouple Error and
RMS Noise vs Temperature
Type T Thermocouple Error and
RMS Noise vs Temperature
TYPICAL PERFORMANCE CHARACTERISTICS
Type J Thermocouple Error and
RMS Noise vs Temperature
Type K Thermocouple Error and
RMS Noise vs Temperature
Type N Thermocouple Error and
RMS Noise vs Temperature
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G01
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 800 1200 16004000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G02
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 800 1200 16004000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G03
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 800 1200 16004000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G04
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 800 1200 1600 20004000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G05
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 800 1200 1600 20004000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G06
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 200 400 6000–200
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G07
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 400 800 12000
RMS NOISE
ERROR
THERMOCOUPLE TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G08
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
400 1200 1600 2000800
RMS NOISE
ERROR
RTD TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G09
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 400 8000
RMS NOISE
ERROR
T
LTC2983
L7 LJUW 7
LTC2983
7
2983fc
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TYPICAL PERFORMANCE CHARACTERISTICS
RTD PT-200 Error and RMS Noise
vs Temperature
RTD PT-100 Error and RMS Noise
vs Temperature
RTD NI-120 RTD Error and
RMS Noise vs Temperature
RTD TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G10
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 400 8000
RMS NOISE
ERROR
RTD TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G11
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–400 0 200 400 600 800 1000–200
RMS NOISE
ERROR
RTD TEMPERATURE (°C)
ERROR/RMS NOISE (°C)
2983 G12
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
–100 0 100 200 300
RMS NOISE
ERROR
5k Thermistor Error vs Temperature
10k Thermistor Error vs Temperature
3k Thermistor Error vs Temperature
30k Thermistor Error vs
Temperature
YSI-400 Thermistor Error vs
Temperature
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G19
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G20
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G21
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G22
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G23
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
THERMISTOR TEMPERATURE (°C)
ERROR (°C)
2983 G24
1.0
0.8
0.6
0.2
0.4
–1.0
–0.8
–0.6
–0.4
–0.2
0
–40 0–20 20 80 1006040 120 140
2.252k Thermistor Error vs
Temperature
LTC2983
INPUT LEAKAGE (HA)
2 3 4
WPUT VOLTAGE (v)
5
5
2 suns
2 sum
25
Vngmur M
245375
24355
fan 730 40 w an 50 70 so m: we
TEMPERATURE m
L7
LINE/“2
v toerch
LTC2983
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2983fc
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TYPICAL PERFORMANCE CHARACTERISTICS
Adjacent Channel Offset Error vs
Input Fault Voltage (VDD = 5V)
Adjacent Channel Offset Error vs
Input Fault Voltage
CH1 FAULT VOLTAGE (V)
CH2 OFFSET ERROR (µV)
2983 G25
2.5
1.5
2.0
–0.5
0
0.5
1.0
4.95 5.055 5.1 5.2 5.255.15 5.3 5.35
CH1 FAULT VOLTAGE (V)
CH2 OFFSET ERROR (µV)
2983 G26
2.5
1.5
2.0
–0.5
0
0.5
1.0
0 –0.05 –0.1 –0.2 –0.25–0.15 –0.3 –0.35
Offset vs Temperature Noise vs Temperature
ISLEEP vs Temperature
One Shot Conversion Current vs
Temperature VREFOUT vs Temperature
LTC2983 TEMPERATURE (°C)
OFFSET (µV)
2983 G13
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–50 –25 50 75250 100 125
VDD = 5.25V
VDD = 4.1V
VDD = 2.85V
LTC2983 TEMPERATURE (°C)
NOISE (µVRMS)
2983 G14
1.2
1.0
0.8
0.6
0.4
0.2
0
–50 500 25–25 10075 125
VDD = 5.25V
VDD = 4.1V
VDD = 2.85V
LTC2983 TEMPERATURE (°C)
ISLEEP (µA)
2983 G15
60
50
40
30
20
10
0
–50 –25 50 75250 100 125
VDD = 5.25V
VDD = 4.1V
VDD = 2.85V
LTC2983 TEMPERATURE (°C)
IIDLE (mA)
2983 G16
16.0
15.8
15.6
15.4
15.2
14.8
14.6
14.4
14.2
15.0
0
–50 50250–25 10075 125
VDD = 5.25V
VDD = 4.1V
VDD = 2.85V
Channel Input Leakage Current vs
Temperature
Diode Error and Repeatability vs
Temperature
DIODE TEMPERATURE (°C)
ERROR (°C)
2983 G27
1.0
0.8
0.6
–0.2
–0.4
–0.6
–0.8
0
0.2
0.4
–1.0
–40 20 80 140
TEMPERATURE (°C)
–50
–30
–10
10
30
50
70
90
110
130
2.4995
2.49975
2.5
2.50025
2.5005
V
REFOUT
(V)
REFOUT
2983 G28
125°C
90°C
25°C
–45°C
INPUT VOLTAGE (V)
–1
0
1
2
3
4
5
6
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
INPUT LEAKAGE (nA)
Temperature
2983 G18
LTC2983
L7 LJUW 9
LTC2983
9
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PIN FUNCTIONS
GND (Pins 1, 3, 5, 7, 9, 12, 15, 44): Ground. Connect
each of these pins to a common ground plane through a
low impedance connection. All eight pins must be grounded
for proper operation.
VDD (Pins 2, 4, 6, 8, 45): Analog Power Supply. Tie all
five pins together and bypass as close as possible to the
device, to ground with a 0.1μF capacitor.
VREF_BYP( Pin 11): Internal Reference Power. This is an
internal supply pin, do not load this pin with external
circuitry. Decouple with a 0.1µF capacitor to GND.
VREFOUT (Pin 13): Reference Output Voltage. Short to
VREFP. A minimum 1μF capacitor to ground is required.
Do not load this pin with external circuitry.
VREFP (Pin 14): Positive Reference Input. Tie to VREFOUT.
CH1 to CH20 (Pin 16 to Pin 35): Analog Inputs. May be
programmed for single-ended, differential, or ratiometric
operation. The voltage on these pins can have any value
between GND – 50mV and VDD – 0.3V. Unused pins can
be grounded or left floating.
COM (Pin 36): Analog Input. The common negative input
for all single-ended configurations. The voltage on this
pin can have any value between GND – 50mV and VDD –
0.3V. This pin is typically tied to ground for temperature
measurements.
INTERRUPT (Pin 37): This pin outputs a LOW when the
device is busy either during start-up or while a conversion
cycle is in progress. This pin goes HIGH at the conclusion
of the start-up state or conversion cycle.
SCK (Pin 38): Serial Clock Pin. Data is shifted out of the
device on the falling edge of SCK and latched by the device
on the rising edge.
SDO (Pin 39): Serial Data Out. During the data output state,
this pin is used as the serial data output. When the chip
select pin is HIGH, the SDO pin is in a high impedance state.
SDI (Pin 40): Serial Data Input. Used to program the device.
Data is latched on the rising edge of SCK.
CS (Pin 41): Active Low Chip Select. A low on this pin
enables the digital input/output. A HIGH on this pin
places SDO in a high impedance state. A falling edge on
CS marks the beginning of a SPI transaction and a rising
edge marks the end.
RESET (Pin 42): Active Low Reset. While this pin is LOW,
the device is forced into the reset state. Once this pin is
returned HIGH, the device initiates its start-up sequence.
LDO (Pin 43): 2.5V LDO Output. Bypass with a 10µF
capacitor to GND. This is an internal supply pin, do not
load this pin with external circuitry.
Q3, Q2, Q1 (Pins 46, 47, 48): External Bypass Pins for
–200mV integrated Charge Pump. Tie a 10µF X7R capaci-
tor between Q1 and Q2 close to each pin. Tie a 10µF X5R
capacitor from Q3 to Ground. These are internal supply
pins, do not make additional connections.
LTC2983
LTC2983
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OVERVIEW
The LTC2983 measures temperature using the most com-
mon sensors (thermocouples, RTDs, thermistors, and
diodes). It includes all necessary active circuitry, switches,
measurement algorithms, and mathematical conversions
to determine the temperature for each sensor type.
Thermocouples can measure temperatures from as low as
–265°C to over 1800°C. Thermocouples generate a voltage
as a function of the temperature difference between the tip
(thermocouple temperature) and the electrical connection
on the circuit board (cold junction temperature). In order
to determine the thermocouple temperature, an accurate
measurement of the cold junction temperature is required;
this is known as cold junction compensation. The cold
junction temperature is usually determined by placing a
separate (non-thermocouple) temperature sensor at the
cold junction. The LTC2983 allows diodes, RTDs, and
thermistors to be used as cold junction sensors. In order
to convert the voltage output from the thermocouple into
a temperature result, a high order polynomial equation (up
to 14th order) must be solved. The LTC2983 has these
polynomials built in for virtually all standard thermocouples
(J, K, N, E, R, S, T, and B). Additionally, inverse polyno-
mials must be solved for the cold junction temperature.
The LTC2983 simultaneously measures the thermocouple
output and the cold junction temperature and performs
all required calculations to report the thermocouple tem-
perature in °C or °F. It directly digitizes both positive and
negative voltages (down to 50mV below ground) from a
single ground referenced supply, includes sensor burn-
out detection, and allows external protection/anti-aliasing
circuits without the need of buffer circuits.
Diodes are convenient low cost sensor elements and
are often used to measure cold junction temperatures in
thermocouple applications. Diodes are typically used to
measure temperatures from –60°C to 130°C, which is
suitable for most cold junction applications. Diodes gen-
erate an output voltage that is a function of temperature
and excitation current. When the difference of two diode
output voltages are taken at two different excitation current
levels, the result (∆VBE) is proportional to temperature.
The LTC2983 accurately generates excitation currents,
measures the diode voltages, and calculates the tempera-
ture in °C or °F.
RTDs and thermistors are resistors that change value as a
function of temperature. RTDs can measure temperatures
over a wide temperature range, from as low as –200°C
to 850°C while thermistors typically operate from –40°C
to 150°C. In order to measure one of these devices a
precision sense resistor is tied in series with the sensor.
An excitation current is applied to the network and a ra-
tiometric measurement is made. The value, in Ω, of the
RTD/thermistor can be determined from this ratio. This
resistance is used to determine the temperature of the
sensor element using a table lookup (RTDs) or solving
Steinhart-Hart equations (thermistors). The LTC2983 auto-
matically generates the excitation current, simultaneously
measures the sense resistor and thermistor/RTD voltage,
calculates the sensor resistance and reports the result
in °C. The LTC2983 can digitize most RTD types (PT-10,
PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120), has
built in coefficients for many curves (American, European,
Japanese, and ITS-90), and accommodates 2-wire, 3-wire,
and 4-wire configurations. It also includes coefficients for
calculating the temperature of standard 2.252k, 3k, 5k,
10k , and 30k thermistors. It can be configured to share
one sense resistor among multiple RTDs/thermistors and
to rotate excitation current sources to remove parasitic
thermal effects.
In addition to built-in linearization coefficients, the LTC2983
provides the means of inserting custom coefficients for
both RTDs and thermistors.
LTC2983
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OVERVIEW
Table 1. LTC2983 Error Contribution and Peak Noise Errors
SENSOR TYPE TEMPERATURE RANGE ERROR CONTRIBUTION PEAK-TO-PEAK NOISE
Type K Thermocouple –200°C to 0°C
0°C to 1372°C
±(Temperature • 0.23% + 0.05)°C
±(Temperature • 0.12% + 0.05)°C ±0.08°C
Type J Thermocouple –210°C to 0°C
0°C to 1200°C
±(Temperature • 0.23% + 0.05)°C
±(Temperature • 0.10% + 0.05)°C ±0.07°C
Type E Thermocouple –200°C to 0°C
0°C to 1000°C
±(Temperature • 0.18% + 0.05)°C
±(Temperature • 0.10% + 0.05)°C ±0.06°C
Type N Thermocouple –200°C to 0°C
0°C to 1300°C
±(Temperature • 0.27% + 0.08)°C
±(Temperature • 0.10% + 0.08)°C ±0.13°C
Type R Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C
Type S Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C
Type B Thermocouple 400°C to 1820°C ±(Temperature • 0.10%)°C ±0.83°C
Type T Thermocouple –250°C to 0°C
0°C to 400°C
±(Temperature • 0.15% + 0.05)°C
±(Temperature • 0.10% + 0.05)°C ±0.09°C
External Diode (2 Reading) –40°C to 85°C ±0.25°C ±0.05°C
External Diode (3 Reading) –40°C to 85°C ±0.25°C ±0.2°C
Platinum RTD - PT-10, RSENSE = 1kΩ
Platinum RTD - PT-100, RSENSE = 2kΩ
Platinum RTD - PT-500, RSENSE = 2kΩ
Platinum RTD - PT-1000, RSENSE = 2kΩ
–200°C to 800°C
–200°C to 800°C
–200°C to 800°C
–200°C to 800°C
±0.1°C
±0.1°C
±0.1°C
±0.1°C
±0.05°C
±0.05°C
±0.02°C
±0.01°C
Thermistor, RSENSE = 10kΩ –40°C to 85°C ±0.1°C ±0.01°C
Table 1 shows the estimated system accuracy and noise
associated with specific temperature sensing devices.
System accuracy and peak-to-peak noise include the effects
of the ADC, internal amplifiers, excitation current sources,
and integrated reference for I-grade parts. Accuracy
and noise are the worst-case errors calculated from the
guaranteed maximum ADC and reference specifications.
Peak-to-peak noise values are calculated at 0°C (except
type B was calculated at 400°C) and diode measurements
use AVG = ON mode.
Thermocouple errors do not include the errors associated
with the cold junction measurement. Errors associated
with a specific cold junction sensor within the operating
temperature range can be combined with the errors for a
given thermocouple for total temperature measurement
accuracy.
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Table 2A. Memory Map
LTC2983 MEMORY MAP
SEGMENT START
ADDRESS
END
ADDRESS
SIZE
(BYTES)
DESCRIPTION
Command Status Register 0x000 0x000 1 See Table 6, Initiate Conversion, Sleep Command
Reserved 0x001 0x00F 15
Temperature Result Memory
20 Words - 80 Bytes
0x010 0x05F 80 See Tables 8 to 10, Read Result
Reserved 0x060 0x0EF 144
Global Configuration Register 0x0F0 0x0F0 1
Reserved 0x0F1 0x0F3 3
Measure Multiple Channels Bit Mask 0x0F4 0x0F7 4 See Tables 65, 66, Run Multiple Conversions
Reserved 0x0F8 0x0F8 1
Reserved 0x0F9 0x0FE 6
Mux Configuration Delay 0x0FF 0x0FF 1 See MUX Configuration Delay Section of Data Sheet
Reserved 0x100 0x1FF 256
Channel Assignment Data 0x200 0x24F 80 See Tables 3, 4, Channel Assignment
Custom Sensor Table Data 0x250 0x3CF 384
Reserved 0x3D0 0x3FF 48
OVERVIEW
Memory Map
The LTC2983 channel assignment, configuration, conver-
sion start, and results are all accessible via the RAM (see
Table 2A). Table 2B details the valid SPI instruction bytes
for accessing memory. The channel conversion results are
mapped into memory locations 0x010 to 0x05F and can be
read using the SPI interface as shown in Figure 1. A read is
initiated by sending the read instruction byte = 0x03
followed by the address and then data. Channel assign-
ment data resides in memory locations 0x200 to 0x24F
and can be programmed via the SPI interface as shown in
Figure 2. A write is initiated by sending the write instruc-
tion byte = 0x02 followed by the address and then data.
Conversions are initiated by writing the conversion control
byte (see Table 6) into memory location 0x000 (command
status register).
Table 2B. SPI Instruction Byte
INSTRUCTION SPI INSTRUCTION BYTE DESCRIPTION
Read 0b00000011 See Figure 1
Write 0b00000010 See Figure 2
No Opp 0bXXXXXX0X
LTC2983
_l I—
W
IVTII||||||||||\|||||||||\
j I—
W
IWII||||||||||\|||||||||\||||||||
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OVERVIEW
Figure 2. Memory Write Operation
Figure 1. Memory Read Operation
SCK
CS
RECEIVER SAMPLES
DATA ON RISING EDGE
TRANSMITTER TRANSITIONS
DATA ON FALLING EDGE
SDI I7 I6 I5 I4 I3 I2 I1 I0
00000011
0 0 0 0 A11 A10 A9 A8
16-BIT ADDRESS FIELD
USER MEMORY READ TRANSACTION
FIRST DATA BYTE
SUBSEQUENT
DATA BYTES
MAY FOLLOW
SPI INSTRUCTION BYTE
READ = 0x03
A7 A6 A5 A4 A3 A2 A1 A0
SDO
2983 F01
D7 D6 D5 D4 D3 D2 D1 D0
• • •
• • •
SCK
CS
RECEIVER SAMPLES
DATA ON RISING EDGE
TRANSMITTER TRANSITIONS
DATA ON FALLING EDGE
SDI I7 I6 I5 I4 I3 I2 I1 I0
00000010
0 0 0 0 A11 A10 A9 A8
16-BIT ADDRESS FIELD
USER MEMORY WRITE TRANSACTION
FIRST DATA BYTE
SUBSEQUENT
DATA BYTES
MAY FOLLOW
SPI INSTRUCTION BYTE
WRITE = 0x02
A7 A6 A5 A4 A3 A2 A1 A0
2983 F02
• • •
D7 D6 D5 D4 D3 D2 D1 D0 • • •
LTC2983
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APPLICATIONS INFORMATION
The LTC2983 combines high accuracy with ease of use.
The basic operation is simple and is composed of five
states (see Figure 3).
applicable). The user is locked out of RAM access while
in the state (except for reading status location 0x000).
The end of conversion is indicated by both the INTER-
RUPT pin going HIGH and a status register START bit
going LOW and DONE bit going HIGH.
5. Read Results. In this state, the user has access to
RAM and can read the completed conversion results
and fault status bits. It is also possible for the user to
modify/append the channel assignment data during the
read results state.
Conversion State Details
State 1: Start-Up
The start-up state automatically occurs when power is ap-
plied to the LTC2983. If the power drops below a threshold
of ≈2.6V and then returns to the normal operating voltage
(2.85V to 5.25V), the LTC2983 resets and enters the power-
up state. Note that the LTC2983 also enters the start-up
state at the conclusion of the sleep state. The start-up state
can also be entered at any time during normal operation
by pulsing the RESET pin low.
In the first phase of the start-up state all critical analog
circuits are powered up. This includes the LDO, reference,
charge pump and ADCs. During this first phase, the com-
mand status register will be inaccessible to the user. This
phase takes a maximum of 100mS to complete. Once this
phase completes, the command status register will be
accessible and return a value of 0x80 until the LTC2983
is completely initialized. Once the LTC2983 is initialized
and ready to use, the interrupt pin will go high and the
command status register will return a read value of 0x40
(Start bit=0, Done bit=1). At this point the LTC2983
is fully initialized and is ready to perform a conversion.
State 2: Channel Assignment
The LTC2983 RAM can be programmed with up to 20 sets
of 32-bit (4-byte) channel assignment data. These reside
sequentially in RAM with a one-to-one correspondence
to each of the 20 analog input channels (see Table 3).
Channels that are not used should have their channel
assignment data set to all zeros (default at START-UP).
The channel assignment data contains all the necessary
information associated with the specific sensor tied to that
channel (see Table 4). The first five bits determine the sensor
type (see Table 5). Associated with each sensor are sensor
Figure 3. Basic Operation
2983 F03
POWER-UP,
SLEEP
OR RESET
(OPTIONAL)
≈ 200ms(MAX)
NO
YES
START-UP
CHANNEL ASSIGNMENT
INITIATE CONVERSION
CONVERSION
READ RESULTS
STATUS CHECK
COMPLETE?
Conversion States Overview
1. Start-Up. After power is applied to the LTC2983
(VDD>2.6V), there is a 200ms wake up period. During
this time, the LDO, charge pump, ADCs, and reference
are powered up and the internal RAM is initialized. Once
start-up is complete, the INTERRUPT pin goes HIGH
and the command status register will return a value of
0x40 (Start bit=0, Done bit=1) when read.
2. Channel Assignment. The device automatically enters
the channel assignment state after start-up is complete.
While in this state, the user writes sensor specific data
for each input channel into RAM. The assignment data
contains information about the sensor type, pointers to
cold junction sensors or sense resistors, and sensor
specific parameters.
3. Initiate Conversion. A conversion is initiated by writing
a measurement command into RAM memory location
0x000. This command is a pointer to the channel in
which the conversion will be performed.
4. Conversion. A new conversion begins automatically
following an Initiate Conversion command. In this state,
the ADC is running a conversion on the specified chan-
nel and associated cold junction or RSENSE channel (if
LTC2983
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Table 3. Channel Assignment Memory Map
CHANNEL ASSIGNMENT
NUMBER
CONFIGURATION
DATA START
ADDRESS
CONFIGURATION
DATA
ADDRESS + 1
CONFIGURATION
DATA
ADDRESS + 2
CONFIGURATION
DATA END
ADDRESS + 3
SIZE (BYTES)
CH1 0x200 0x201 0x202 0x203 4
CH2 0x204 0x205 0x206 0x207 4
CH3 0x208 0x209 0x20A 0x20B 4
CH4 0x20C 0x20D 0x20E 0x20F 4
CH5 0x210 0x211 0x212 0x213 4
CH6 0x214 0x215 0x216 0x217 4
CH7 0x218 0x219 0x21A 0x21B 4
CH8 0x21C 0x21D 0x21E 0x21F 4
CH9 0x220 0x221 0x222 0x223 4
CH10 0x224 0x225 0x226 0x227 4
CH11 0x228 0x229 0x22A 0x22B 4
CH12 0x22C 0x22D 0x22E 0x22F 4
CH13 0x230 0x231 0x232 0x233 4
CH14 0x234 0x235 0x236 0x237 4
CH15 0x238 0x239 0x23A 0x23B 4
CH16 0x23C 0x23D 0x23E 0x23F 4
CH17 0x240 0x241 0x242 0x243 4
CH18 0x244 0x245 0x246 0x247 4
CH19 0x248 0x249 0x24A 0x24B 4
CH20 0x24C 0x24D 0x24E 0x24F 4
APPLICATIONS INFORMATION
Table 4. Channel Assignment Data
SENSOR TYPE SENSOR SPECIFIC CONFIGURATION
Channel
Assignment
Memory Location
Configuration Data
Start Address
Configuration Data
Start Address + 1
Configuration Data
Start Address + 2
Configuration Data
Start Address + 3
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Unassigned
(Default)
Type = 0 Channel Disabled
Thermocouple Type = 1 to 9 Cold Junction Channel
Assignment [4:0]
SGL=1
DIFF=0
OC
Check
OC Current
[1:0]
0 0 0 0 0 0 Custom
Address [5:0]
Custom
Length - 1 [5:0]
RTD Type = 10 to 18 RSENSE Channel Assignment
[4:0]
2, 3, 4 Wire Excitation
Mode
Excitation
Current [3:0]
Curve
[1:0]
Custom
Address [5:0]
Custom
Length - 1 [5:0]
Thermistor Type = 19 to 27 RSENSE Channel Assignment
[4:0]
SGL=1
DIFF=0
Excitation
Mode
Excitation Current
[3:0]
0 0 0 Custom
Address [5:0]
Custom
Length - 1 [5:0]
Diode Type = 28 SGL=1
DIFF=0
2 to 3
Reading
Avg
on
Current
[1:0]
Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution
All Zeros Use Factory Set Default in ROM
Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to 131,072Ω with 1/1024Ω Resolution
Direct ADC Type = 30 SGL=1
DIFF=0
Not Used
Reserved Type = 31 Not Used
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APPLICATIONS INFORMATION
specific configurations. These include pointers to cold junction
or sense resistor channels, pointers to memory locations of
custom linearization data, sense resistor values and diode
ideality factors. Also included in this data are, if applicable, the
excitation current level, single-ended/differential input mode,
as well as sensor specific controls. Separate detailed operation
sections for thermocouples, RTDs, diodes, thermistors, and
sense resistors describe the assignment data associated with
each sensor type in more detail. The LTC2983 demonstration
Table 5. Sensor Type Selection
31 30 29 28 27 SENSOR TYPE
0 0 0 0 0 Unassigned
0 0 0 0 1 Type J Thermocouple
0 0 0 1 0 Type K Thermocouple
0 0 0 1 1 Type E Thermocouple
0 0 1 0 0 Type N Thermocouple
0 0 1 0 1 Type R Thermocouple
0 0 1 1 0 Type S Thermocouple
0 0 1 1 1 Type T Thermocouple
0 1 0 0 0 Type B Thermocouple
0 1 0 0 1 Custom Thermocouple
0 1 0 1 0 RTD PT-10
0 1 0 1 1 RTD PT-50
0 1 1 0 0 RTD PT-100
0 1 1 0 1 RTD PT-200
0 1 1 1 0 RTD PT-500
0 1 1 1 1 RTD PT-1000
1 0 0 0 0 RTD 1000 (0.00375)
1 0 0 0 1 RTD NI-120
1 0 0 1 0 RTD Custom
1 0 0 1 1 Thermistor 44004/44033 2.252kΩ at 25°C
10 1 0 0 Thermistor 44005/44030 3kΩ at 25°C
1 0 1 0 1 Thermistor 44007/44034 5kΩ at 25°C
1 0 1 1 0 Thermistor 44006/44031 10kΩ at 25°C
1 0 1 1 1 Thermistor 44008/44032 30kΩ at 25°C
1 1 0 0 0 Thermistor YSI 400 2.252kΩ at 25°C
1 1 0 0 1 Thermistor Spectrum 1003k 1kΩ
1 1 0 1 0 Thermistor Custom Steinhart-Hart
1 1 0 1 1 Thermistor Custom Table
1 1 1 0 0 Diode
1 1 1 0 1 Sense Resistor
1 1 1 1 0 Direct ADC
1 1 1 1 1 Reserved
Table 7. Input Channel Mapping
B7 B6 B5 B4 B3 B2 B1 B0 CHANNEL SELECTED
1 0 0 0 0 0 0 0 Multiple Channels
1 0 0 0 0 0 0 1 CH1
1 0 0 0 0 0 1 0 CH2
1 0 0 0 0 0 1 1 CH3
1 0 0 0 0 1 0 0 CH4
1 0 0 0 0 1 0 1 CH5
1 0 0 0 0 1 1 0 CH6
1 0 0 0 0 1 1 1 CH7
1 0 0 0 1 0 0 0 CH8
1 0 0 0 1 0 0 1 CH9
1 0 0 0 1 0 1 0 CH10
1 0 0 0 1 0 1 1 CH11
100011 0 0 CH12
1 0 0 0 1 1 0 1 CH13
1 0 0 0 1 1 1 0 CH14
1 0 0 0 1 1 1 1 CH15
1 0 0 1 0 0 0 0 CH16
1 0 0 1 0 0 0 1 CH17
1 0 0 1 0 0 1 0 CH18
1 0 0 1 0 0 1 1 CH19
1 0 0 1 0 1 0 0 CH20
1 0 0 1 0 1 1 1 Sleep
All Other Combinations Reserved
Table 6. Command Status Register
B7 B6 B5 B4 B3 B2 B1 B0
Start = 1 Done = 0 0 Channel Selection 1 to 20 Start Conversion
1 0 0 1 0 1 1 1 Initiate Sleep
software includes a utility for checking configuration data and
generating annotated C-code for programming the channel
assignment data.
State 3: Initiate Conversion
Once the channel assignment is complete, the device is
ready to begin a conversion. A conversion is initiated by
writing Start (B7=1) and Done (B6=0) followed by the
desired input channel (B4 – B0) into RAM memory loca-
tion 0x000 (see Tables 6 and 7). It is possible to initiate
a measurement cycle on multiple channels by setting the
channel selection bits (B4 to B0) to 00000; see the Running
Conversions Consecutively on Multiple Channels section
of the data sheet.
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APPLICATIONS INFORMATION
Bits B4 to B0 determine which input channel the conversion
is performed upon and are simply the binary equivalent
of the channel number (see Table 7).
Bit B5 should be set to 0.
Bits B7 and B6 serve as start/done bits. In order to start
a conversion, these bits must be set to “10” (B7=1 and
B6=0). When the conversion begins, the INTERRUPT
pin goes LOW. Once the conversion is complete, bits B7
and B6 will toggle to “01” (B7=0 and B6=1) (Address =
0x000) and the INTERRUPT pin will go HIGH, indicating
the conversion is complete and the result is available.
State 4: Conversion
The measurement cycle starts after the initiate conversion
command is written into RAM location 0x000 (Table 6).
The LTC2983 simultaneously measures the selected input
sensor, sense resistors (RTDs and thermistors), and cold
junction temperatures if applicable (thermocouples).
Once the conversion is started, the user is locked out of
the RAM, with the exception of reading status data stored
in RAM memory location 0x000.
Once the conversion is started the INTERRUPT pin goes
low. Depending on the sensor configuration, two or three
82ms cycles are required per temperature result. These
correspond to conversion rates of 167ms and 251ms,
respectively. Details describing these modes are described
in the 2- and 3-cycle Conversion Modes section of the
data sheet.
The end of conversion can be monitored either through
the interrupt pin (LOW to HIGH transition), or by reading
the command status register in RAM memory location
0x000 (start bit, B7, toggles from 1 to 0 and DONE bit,
B6, toggles from 0 to 1).
State 5: Read Results
Once the conversion is complete, the conversion results
can be read from RAM memory locations corresponding
to the input channel (see Table 8).
The conversion result is 32 bits long and contains both
the sensor temperature (D23 to D0) and sensor fault data
(D31 to D24) (see Tables 9A and 9B).
Table 8. Conversion Result Memory Map
CONVERSION
CHANNEL
START
ADDRESS
END ADDRESS SIZE (BYTES)
CH1 0x010 0x013 4
CH2 0x014 0x017 4
CH3 0x018 0x01B 4
CH4 0x01C 0x01F 4
CH5 0x020 0x023 4
CH6 0x024 0x027 4
CH7 0x028 0x02B 4
CH8 0x02C 0x02F 4
CH9 0x030 0x033 4
CH10 0x034 0x037 4
CH11 0x038 0x03B 4
CH12 0x03C 0x03F 4
CH13 0x040 0x043 4
CH14 0x044 0x047 4
CH15 0x048 0x04B 4
CH16 0x04C 0x04F 4
CH17 0x050 0x053 4
CH18 0x054 0x057 4
CH19 0x058 0x05B 4
CH20 0x05C 0x05F 4
The result is reported in °C for all temperature sensors with a
range of –273.16°C to 8192°C and 1/1024°C resolution or in
°F with a range of –459.67°F to 8192°F with 1/1024°F reso-
lution. Included with the conversion result are seven sensor
fault bits and a valid bit. These bits are set to a 1 if there was a
problem associated with the corresponding conversion result
(see Table 10). Two types of errors are reported: hard errors
and soft errors. Hard errors indicate the reading is invalid
and the resulting temperature reported is –999°C or °F. Soft
errors indicate operation beyond the normal temperature
range of the sensor or the input range of the ADC. In this
case, the calculated temperature is reported but the ac-
curacy may be compromised. Details relating to each fault
type are sensor specific and are described in detail in the
sensor specific sections of this data sheet. Bit D24 is the
valid bit and will be set to a 1 for valid data.
Once the data read is complete, the device is ready for a new
initiate conversion command. In cases where new channel
configuration data is required, the user has access to the
RAM in order to modify existing channel assignment data.
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Table 9A. Example Data Output Words (°C)
START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3
(END ADDRESS)
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Fault Data SIGN MSB LSB
Temperature Sensor
Hard
Fault
ADC
Hard
Fault
CJ
Hard
Fault
CJ
Soft
Fault
Sensor
Over
Range
Fault
Sensor
Under
Range
Fault
ADC
Out
of
Range
Fault
Valid
If 1 4096°C 1°C 1/1024°C
8191.999°C 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1024°C 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
1/1024°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–1/1024°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
–1°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
–273.15°C 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1
Table 9B. Example Data Output Words (°F)
START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3
(END ADDRESS)
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Fault Data SIGN MSB LSB
Temperature Sensor
Hard
Fault
ADC
Hard
Fault
CJ
Hard
Fault
CJ
Soft
Fault
Sensor
Over
Range
Fault
Sensor
Under
Range
Fault
ADC
Out
of
Range
Fault
Valid
If 1 4096°F 1°F 1/1024°F
8191.999°F 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1024°F 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
1/1024°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–1/1024°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
–1°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
–459.67°F 1 1 1 1 1 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0
Table 10. Sensor Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Bad Sensor Reading –999°C or °F
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F
D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F
D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading
D27 Sensor Over Range Soft Sensor Reading Is Above Normal Range Suspect Reading
D26 Sensor Under Range Soft Sensor Reading Is Below Normal Range Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading
D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Suspect Reading
APPLICATIONS INFORMATION
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Table 13. Cold Junction Channel Pointer
(2) COLD JUNCTION CHANNEL POINTER
B26 B25 B24 B23 B22 COLD JUNCTION CHANNEL
0 0 0 0 0 No Cold Junction
Compensation, 0°C Used for
Calculations
0 0 0 0 1 CH1
0 0 0 1 0 CH2
0 0 0 1 1 CH3
0 0 1 0 0 CH4
0 0 1 0 1 CH5
0 0 1 1 0 CH6
0 0 1 1 1 CH7
0 1 0 0 0 CH8
0 1 0 0 1 CH9
0 1 0 1 0 CH10
0 1 0 1 1 CH11
0 1 1 0 0 CH12
0 1 1 0 1 CH13
0 1 1 1 0 CH14
0 1 1 1 1 CH15
1 0 0 0 0 CH16
10 0 0 1 CH17
1 0 0 1 0 CH18
1 0 0 1 1 CH19
1 0 1 0 0 CH20
All Other Combinations Invalid
THERMOCOUPLE MEASUREMENTS
Table 12. Thermocouple Type
(1) THERMOCOUPLE TYPE
B31 B30 B29 B28 B27 THERMOCOUPLE TYPES
0 0 0 0 1 Type J Thermocouple
0 0 0 1 0 Type K Thermocouple
0 0 0 1 1 Type E Thermocouple
0 0 1 0 0 Type N Thermocouple
0 0 1 0 1 Type R Thermocouple
0 0 1 1 0 Type S Thermocouple
0 0 1 1 1 Type T Thermocouple
0 1 0 0 0 Type B Thermocouple
0 1 0 0 1 Custom Thermocouple
Table 11. Thermocouple Channel Assignment Word
(1) THERMOCOUPLE
TYPE
(2) COLD JUNCTION
CHANNEL POINTER
(3) SENSOR
CONFIGURATION
(4) CUSTOM THERMOCOUPLE
DATA POINTER
TABLES 4, 12 TABLE 13 TABLE 14 TABLES 67 TO 69
Measurement Type 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Thermocouple Types 1 to 9 Cold Junction
Channel Assignment
[4:0]
SGL=1
DIFF=0
OC
Check
OC
Current
[1:0]
0 0 0 0 0 0 Custom Address
[5:0]
Custom Length –1
[5:0]
APPLICATIONS INFORMATION
sensor is assigned to (see Table 13). When a conversion
is performed on a channel tied to a thermocouple, the
cold junction sensor is simultaneously and automatically
measured. The final output data uses the embedded coef-
ficients stored in ROM to automatically compensate the
cold junction temperature and output the thermocouple
sensor temperature.
Channel Assignment – Thermocouples
For each thermocouple tied to the LTC2983, a 32-bit channel
assignment word is programmed into a memory location
corresponding to the channel the sensor is tied to (see
Table 11). This word includes (1) thermocouple type, (2)
cold junction channel pointer, (3) sensor configuration,
and (4) custom thermocouple data pointer.
(1) Thermocouple Type
The thermocouple type is determined by the first five in-
put bits B31 to B27 as shown in Table 12. Standard NIST
coefficients for types J,K,E,N,R,S,T and B thermocouples
are stored in the device ROM. If custom thermocouples
are used, the custom thermocouple sensor type can be
selected. In this case, user-specific data can be stored in
the on-chip RAM starting at the address defined in the
custom thermocouple data pointer.
(2) Cold Junction Channel Pointer
The cold junction compensation can be a diode, RTD,
or thermistor. The cold junction channel pointer tells
the LTC2983 which channel (1 to 20) the cold junction
LTC2983
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Table 14. Sensor Configuration
(3) SENSOR CONFIGURATION
SGL OC
CHECK
OC CURRENT SINGLE-ENDED/
DIFFERENTIAL
OPEN-CIRCUIT
CURRENT
B21 B20 B19 B18
0 0 X X Differential External
0 1 0 0 Differential 10µA
0 1 0 1 Differential 100µA
0 1 1 0 Differential 500µA
0 1 1 1 Differential 1mA
1 0 X X Single-Ended External
1 1 0 0 Single-Ended 10µA
1 1 0 1 Single-Ended 100µA
1 1 1 0 Single-Ended 500µA
1 1 1 1 Single-Ended 1mA
APPLICATIONS INFORMATION
(3) Sensor Configuration
The sensor configuration field (see Table 14) is used
to select single-ended (B21=1) or differential (B21=0)
input and allows selection of open circuit current
if internal open-circuit detect is enabled (bit B20).
Single-ended readings are measured relative to the
COM pin and differential are measured between the
selected CHTC and adjacent CHTC-1 (see Figure 4).
If open-circuit detection is enabled, B20=1, then the user
can select the pulsed current value applied during open-
circuit detect using bits B18 and B19 . The user determines
the value of the open circuit current based on the size of
the external protection resistor and filter capacitor (typically
10µA). This network needs to settle within 50ms to 1µV
or less. The duration of the current pulse is approximately
8ms and occurs 50ms before the normal conversion cycle.
Thermocouple channel assignments follow the general
convention shown in Figure 4. The thermocouple positive
terminal ties to CHTC (where TC is the selected channel
number) for both the single-ended and differential modes
of operation. For single-ended measurements the thermo-
couple negative terminal and the COM pin are grounded.
The thermocouple negative terminal is tied to CHTC-1
for differential measurements. This node can either be
grounded or tied to a bias voltage.
(4) Custom Thermocouple Data Pointer
See Custom Thermocouples section near the end of this
data sheet for more information.
Figure 4. Thermocouple Channel Assignment Convention
SINGLE-ENDED
+
–
+
–
= CHTC (1≤ TC ≤ 20)
COM
CHTC
0.1µF
CHANNEL
ASSIGNMENT
DIFFERENTIAL
2983 F04
= CHTC (2≤ TC ≤ 20)
CHTC
CHTC-1
0.1µF
CHANNEL
ASSIGNMENT
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Table 15. Thermocouple Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open Circuit or Hard ADC or Hard CJ –999°C or °F
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F
D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F
D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading
D27 Sensor Over Range Soft Thermocouple Reading Greater Than High Limit Suspect Reading
D26 Sensor Under Range Soft Thermocouple Reading Less Than Low Limit Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading
D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading
APPLICATIONS INFORMATION
Fault Reporting – Thermocouple
Each sensor type has a unique fault reporting mechanism
indicated in the upper byte of the data output word. Table 15
shows faults reported in the measurement of thermo-
couples.
Bit D31 indicates the thermocouple sensor is open (broken
or not plugged in), the cold junction sensor has a hard
fault, or the ADC is out of range. This is indicated by a
reading well beyond the normal operating range. Bit D30
indicates a bad ADC reading. This can be a result of either
a broken (open) sensor or an excessive noise event (ESD
or static discharge into the sensor path). Either of these
are a hard error and –999°C or °F is reported. In the case
of an excessive noise event, the device should recover and
the following conversions will be valid if the noise event
was a random, infrequent event. Bit D29 indicates a hard
fault occurred at the cold junction sensor and –999°C
or °F is reported. Refer to the specific sensor (diode,
themistor, or RTD) used for cold junction compensation.
Bit D28 indicates a soft fault occurred at the cold junction
sensor. A valid temperature is reported, but the accuracy
may be compromised since the cold junction sensor is
operating outside its normal temperature range. Bits
D27 and D26 indicate over or under temperature limits
have been exceeded for specific thermocouple types, as
defined in Table 16. Bit D25 indicates the absolute voltage
measured by the ADC is beyond its normal operating range.
This fault reflects a reading that is well beyond the normal
range of a thermocouple.
Table 16. Thermocouple Temperature Limits
THERMOCOUPLE TYPE LOW TEMP LIMIT °C HIGH TEMP LIMIT °C
J-Type –210 1200
K-Type –265 1372
E-Type –265 1000
N-Type –265 1300
R-type –50 1768
S-Type –50 1768
T-Type –265 400
B-Type 40 1820
Custom Lowest Table Entry Highest Table Entry
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Table 18. Diode Sensor Selection
(1) SENSOR TYPE
B31 B30 B29 B28 B27 SENSOR TYPE
1 1 1 0 0 Diode
Table 19. Diode Excitation Current Selection
(3) EXCITATION CURRENT
B23 B22 1I 4I 8I
0 0 10µA 40µA 80µA
0 1 20µA 80µA 160µA
1 0 40µA 160µA 320µA
1 1 80µA 320µA 640µA
DIODE MEASUREMENTS
Table 20. Programming Diode Ideality Factor
(4) DIODE IDEALITY FACTOR VALUE
B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Example h21202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 2–11 2–12 2–13 2–14 2–15 2–16 2–17 2–18 2–19 2–20
1.25 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1.003 (Default) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1.006 0 1 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 1
Bit B24 enables a running average of the diode temperature
reading. This reduces the noise when the diode is used
as a cold junction temperature element on an isothermal
block where temperatures change slowly.
The algorithm used for diode averaging is a simple recursive
running average. The new value is equal to the average of
the current reading plus the previous value.
NEW VALUE = CURRENT READING
2
+ PREVIOUS VALUE
2
If the current reading is 2°C above or below the previous
value, the new value is reset to the current reading.
(3) Excitation Current
The next field in the channel assignment word (B23 to B22)
controls the magnitude of the excitation current applied to the
diode (see Table 19). In the two conversion cycle mode, the
device performs the first conversion at a current equal to 8x
the excitation current 1I. The second conversion occurs at 1I.
Alternatively, in the three conversion cycle mode the first
conversion excitation current is 8I, the second is 4I and
the 3rd is 1I.
APPLICATIONS INFORMATION
(2) Sensor Configuration
The sensor configuration field (bits B26 to B24) is used to
define various diode measurement properties. Configura-
tion bit B26 is set high for single-ended (measurement
relative to COM) and low for differential.
Bit B25 sets the measurement algorithm. If B25 is low, two
conversion cycles (one at 1I and one at 8I current excitation)
are used to measure the diode. This is used in applications
where parasitic resistance between the LTC2983 and the
diode is small. Parasitic resistance effects can be removed
by setting bit B25 high, enabling three conversion cycles
(one at 1I, one at 4I and one at 8I).
Table 17. Diode Channel Assignment Word
(1) SENSOR TYPE (2) SENSOR
CONFIGURATION
(3) EXCITATION
CURRENT
(4) DIODE IDEALITY FACTOR VALUE
TABLE 18 TABLE 19 TABLE 20
Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Diode Type = 28 SGL=1
DIFF=0
2 or 3
Readings
Avg
on
Current [1:0] Non-Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution
All Zeros Uses a Factory Set Default of 1.003
Channel Assignment – Diode
For each diode tied to the LTC2983, a 32-bit channel as-
signment word is programmed into a memory location
corresponding to the channel the sensor is tied to (see
Table 17). This word includes (1) diode sensor selection,
(2) sensor configuration, (3) excitation current, and (4)
diode ideality factor.
1) Sensor Type
The diode is selected by the first five input bits B31 to
B27 (see Table 18).
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(4) Diode Ideality Factor
The last field in the channel assignment word (B21 to B0)
sets the diode ideality factor within the range 0 to 4 with
1/1048576 (2–20) resolution. The top two bits (B21 to B20)
are the integer part and bits B19 to B0 are the fractional
part of the ideality factor (see Table 20).
Diode channel assignments follow the general convention
shown in Figure 5. The anode ties to CHD (where D is
the selected channel number) for both the single-ended
and differential modes of operation, and the cathode is
grounded. For differential diode measurements, the cathode
is also tied to CHD-1.
Fault Reporting - Diode
Each sensor type has unique fault reporting mechanism
indicated in the upper byte of the data output word.
Table 21 shows faults reported in the measurement of
diodes.
Bit D31 indicates the diode is open, shorted, not plugged
in, wired backwards, or the ADC reading is bad. Any of
these are hard faults and –999°C or °F is reported. Bit
D30 indicates a bad ADC reading. This can be a result of
either a broken (open) sensor or an excessive noise event
(ESD or static discharge into the sensor path). This is a
APPLICATIONS INFORMATION
Figure 5. Diode Channel Assignment Convention
hard error and –999°C or °F is reported. In the case of
an excessive noise event, the device should recover and
the following conversions will be valid if the noise event
was a random, infrequent event. Bits D29 and D28 are not
used for diodes. Bits D27 and D26 indicate over or under
temperature limits (defined as T > 130°C or T < –60°C). The
calculated temperature is reported, but the accuracy may
be compromised. Bit D25 indicates the absolute voltage
measured by the ADC is beyond its normal operating range.
If a diode is used as the cold junction element, any hard
or soft error is flagged in the corresponding thermocouple
result (bits D28 and D29 in Table 15).
Table 21. Diode Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open, Short, Reversed, or Hard ADC –999°C or °F
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F
D29 Not Used for Diodes N/A Always 0
D28 Not Used for Diodes N/A Always 0
D27 Sensor Over Range Soft T > 130°C Suspect Reading
D26 Sensor Under Range Soft T < –60°C Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading
D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading
2983 F05
SINGLE-ENDED
= CHD (1≤ D ≤ 20)
COM
CHDCHANNEL
ASSIGNMENT
DIFFERENTIAL
= CHD (2≤ D ≤ 20)
CHD
CHD-1
CHANNEL
ASSIGNMENT
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Example: Single-Ended Type K and Differential Type T
Thermocouples with Shared Diode Cold Junction
Compensation
Figure 6 shows a typical temperature measurement
system where two thermocouples share a single cold
junction diode. In this example, a Type K thermocouple
is tied to CH1 and a Type T thermocouple is tied to CH3
and CH4. They both share a single cold junction diode
with ideality factor of h=1.003 tied to CH2. Channel as-
signment data for both thermocouples and the diode are
APPLICATIONS INFORMATION
shown in Tables 22 to 24. Thermocouple #1 (Type K)
sensor type and configuration data are assigned to CH1.
32-bits of binary configuration data are mapped directly
into memory locations 0x200 to 0x203 (see Table 22).
The cold junction diode sensor type and configuration
data are assigned to CH2. 32-bits of binary configuration
data are mapped directly into memory locations 0x204
to 0x207 (see Table 23). Thermocouple #2 (Type T) sen-
sor type and configuration data are assigned to CH4.
32-bits of binary configuration data are mapped directly
Figure 6. Dual Thermocouple with Diode Cold Junction Example
TYPE K 0.1µF
TYPE T
η = 1.003
2983 F06
TYPE K THERMOCOUPLE ASSIGNED TO CH1 (CHTC=1)
DIODE COLD JUNCTION ASSIGNED TO CH2 (CHD=2)
TYPE T THERMOCOUPLE JUNCTION ASSIGNED TO CH4 (CHTC=4)
CH4
CH3
CH2
CH1
0.1µF COM
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x200 TO 0x203
RESULT MEMORY LOCATIONS 0x010 TO 0x013
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x204 TO 0x207
RESULT MEMORY LOCATIONS 0x014 TO 0x017
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x20C TO 0x20F
RESULT MEMORY LOCATIONS 0x01C TO 0x01F
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Table 22. Thermocouple #1 Channel Assignment (Type K, Cold Junction CH2, Single-Ended, 10µA Open-Circuit Detect)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x200
MEMORY
ADDRESS 0x201
MEMORY
ADDRESS 0x202
MEMORY
ADDRESS 0x203
(1) Thermocouple
Type
Type K 5 00010 0 0 0 1 0
(2) Cold Junction
Channel Pointer
CH2500010 0 0 0 1 0
(3) Sensor
Configuration
Single-Ended,
10µA Open-Circuit
41100 1 1 0 0
Not Used Set These Bits to 0 6 000000 0 0 0 0 0 0
(4) Custom
Thermocouple
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 23. Diode Channel Assignment (Single-Ended 3-Reading, Averaging On, 20µA/80µA Excitation, Ideality Factor = 1.003))
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x204
MEMORY
ADDRESS 0x205
MEMORY
ADDRESS 0x206
MEMORY
ADDRESS 0x207
(1) Sensor Type Diode 5 11100 11100
(2) Sensor
Configuration
Single-Ended,
3-Reading,
Average On
3111 1 1 1
(3) Excitation
Current
20µA, 80µA,
160µA
201 0 1
(4) Ideality Factor 1.003 22 0100000000110001001001 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1
Table 24. Thermocouple #2 Channel Assignment (Type T, Cold Junction CH2, Differential, 100µA Open-Circuit Detect)
CONFIGURATION
FIELD
DESCRIPTION #
BITS
BINARY DATA MEMORY
ADDRESS 0x20C
MEMORY
ADDRESS 0x20D
MEMORY
ADDRESS 0x20E
MEMORY
ADDRESS 0x20F
(1) Thermocouple
Type
Type T 5 00111 0 0 1 1 1
(2) Cold Junction
Channel Pointer
CH2500010 0 0 0 1 0
(3) Sensor
Configuration
Differential,
100µA Open-
Circuit Current
40101 0 1 0 1
Not Used Set These Bits
to 0
6000000 0 0 0 0 0 0
(4) Custom
Thermocouple
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
APPLICATIONS INFORMATION
into memory locations 0x20C to 0x20F (see Table24). A
conversion is initiated on CH1 by writing 10000001 into
memory location 0x000. Both the Type K thermocouple
and the diode are measured simultaneously. The LTC2983
calculates the cold junction compensation and determines
the temperature of the Type K thermocouple. Once the
conversion is complete, the INTERRUPT pin goes HIGH
and memory location 0x000 becomes 01000001. Similarly,
a conversion can be initiated on CH4 by writing 10000100
into memory location 0x000. The results (in °C) can be
read from memory locations 0x010 to 0x013 for CH1 and
0x01C to 0x01F for CH4.
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APPLICATIONS INFORMATION
RTD MEASUREMENTS
(2) Sense Resistor Channel Pointer
RTD measurements are performed ratiometrically relative
to a known RSENSE resistor. The sense resistor channel
pointer field indicates the differential channel the sense
resistor is tied to for the RTD (see Table 27). Sense resis-
tors are always measured differentially.
Table 26. RTD Type
(1) RTD TYPE
B31 B30 B29 B28 B27 RTD TYPE
0 1 0 1 0 RTD PT-10
0 1 0 1 1 RTD PT-50
0 1 1 0 0 RTD PT-100
0 1 1 0 1 RTD PT-200
0 1 1 1 0 RTD PT-500
0 1 1 1 1 RTD PT-1000
1 0 0 0 0 RTD 1000 (α=0.00375)
1 0 0 0 1 RTD NI-120
1 0 0 1 0 RTD Custom
Table 25. RTD Channel Assignment Word
(1) RTD TYPE (2) SENSE RESISTOR
CHANNEL POINTER
(3) SENSOR
CONFIGURATION
(4) EXCITATION
CURRENT
(5) RTD
CURVE
(6) CUSTOM RTD DATA POINTER
TABLE 26 TABLE 27 TABLE 28 TABLE 29 TABLE 30 TABLES 72 TO 74
Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RTD Type = 10 to 18 RSENSE Channel
Assignment [4:0]
2, 3, 4
Wire
Excitation
Mode
Excitation
Current [3:0]
Curve
[1:0]
Custom Address
[5:0]
Custom Length – 1
[5:0]
Table 27. Sense Resistor Channel Pointer
(2) SENSE RESISTOR CHANNEL POINTER
B26 B25 B24 B23 B22 SENSE RESISTOR CHANNEL
0 0 0 0 0 Invalid
0 0 0 0 1 Invalid
0 0 0 1 0 CH2-CH1
0 0 0 1 1 CH3-CH2
0 0 1 0 0 CH4-CH3
0 0 1 0 1 CH5-CH4
0 0 1 1 0 CH6-CH5
0 0 1 1 1 CH7-CH6
0 1 0 0 0 CH8-CH7
0 1 0 0 1 CH9-CH8
0 1 0 1 0 CH10-CH9
0 1 0 1 1 CH11-CH10
0 1 1 0 0 CH12-CH11
0 1 1 0 1 CH13-CH12
0 1 1 1 0 CH14-CH13
0 1 1 1 1 CH15 -CH14
1 0 0 0 0 CH16-CH15
1 0 0 0 1 CH17-CH16
1 0 0 1 0 CH18-CH17
1 0 0 1 1 CH19-CH18
1 0 1 0 0 CH20-CH19
All Other Combinations Invalid
Channel Assignment – RTD
For each RTD tied to the LTC2983, a 32-bit channel as-
signment word is programmed into a memory location
corresponding to the channel the sensor is tied to (see Table
25). This word includes (1) RTD type, (2) sense resistor
channel pointer, (3) sensor configuration, (4) excitation
current, (5) RTD curve, and (6) custom RTD data pointer.
(1) RTD Type
The RTD type is determined by the first five input bits B31
to B27 as shown in Table 26. Linearization coefficients
for RTD types PT-10, PT-50, PT-100, PT-200, PT-500,
PT-1000, and NI-120 with selectable common curves
(α = 0.003850, α = 0.003911, α = 0.003916, and
α = 0.003926) are built into the device. If custom RTDs
are used, RTD Custom can be selected. In this case, user
specific data can be stored in the on-chip RAM starting
at the address defined by the custom RTD data pointers.
LTC2983
L7HEJWEGR 29
LTC2983
29
2983fc
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(3) Sensor Configuration
The sensor configuration field is used to define various
RTD properties. Configuration bits B20 and B21 determine
if the RTD is a 2, 3, or 4 wire type (see Table 28).
The simplest configuration is the 2-wire configuration.
While this setup is simple, parasitic errors due to IR drops
in the leads result in systematic temperature errors. The
3-wire configuration cancels RTD lead resistance errors
(if the lines are equal resistance) by applying two matched
current sources to the RTD, one per lead. Mismatches in
the two current sources are removed through transparent
background calibration. 4-wire RTDs remove unbalanced
RTD lead resistance by measuring directly across the
sensor using a high impedance Kelvin sensing. 4-wire
measurements with Kelvin RSENSE are useful in applica-
tions where sense resistor wiring parasitics can lead to
errors; this is especially useful for low resistance PT-10
type RTDs. In this case, both the RTD and sense resistor
have Kelvin sensing connections.
The next sensor configuration bits (B18 and B19) deter-
mine the excitation current mode. These bits are used to
enable RSENSE sharing, where one sense resistor is used
for multiple 2-, 3-, and/or 4-wire RTDS. In this case, the
RTD ground connection is internal and each RTD points
to the same RSENSE channel.
Table 28. RTD Sensor Configuration Selection
(3) SENSE
CONFIGURATION
MEASUREMENT MODE BENEFITS
NUMBER
OF WIRES
EXCITATION
MODE
NUMBER
OF WIRES
GROUND
CONNECTION
CURRENT
SOURCE
ROTATION
SENSE
RESISTOR
SHARING
RTDs
POSSIBLE
PER
DEVICE
CANCELS RTD
MATCHED
LEAD
RESISTANCE
CANCELS RTD
MISMATCH
LEAD
RESISTANCE
CANCELS
PARASITIC
THERMOCOUPLE
EFFECTS
CANCELS
RSENSE
LEAD
RESISTANCE
B21 B20 B19 B18
0 0 0 0 2-Wire External No No 5
0 0 0 1 2-Wire Internal No Yes 9
0 1 0 0 3-Wire External No No 5 •
0 1 0 1 3-Wire Internal No Yes 9 •
0 1 1 X Reserved
1 0 0 0 4-Wire External No No 4 • •
1 0 0 1 4-Wire Internal No Yes 6 • •
1 0 1 0 4-Wire Internal Yes Yes 6 • • •
1 0 1 1 Reserved
1 1 0 0 4-Wire,
Kelvin
RSENSE
External No No 4 • • •
1 1 0 1 4-Wire,
Kelvin
RSENSE
Internal No Yes 5 • • •
1 1 1 0 4-Wire,
Kelvin
RSENSE
Internal Yes Yes 5 • • • •
1 1 1 1 Reserved
LTC2983
3O L7ELUEN2
LTC2983
30
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Table 29. Total Excitation Current for All RTD Wire Types
(4) EXCITATION CURRENT
B17 B16 B15 B14 CURRENT
0 0 0 0 Reserved
0 0 0 1 5μA
0 0 1 0 10μA
0 0 1 1 25μA
0 1 0 0 50μA
0 1 0 1 100µA
0 1 1 0 250µA
0 1 1 1 500µA
1 0 0 0 1mA
Bits B18 and B19 are also used to enable excitation current
rotation to automatically remove parasitic thermocouple
effects. Parasitic thermocouple effects may arise from the
physical connected between the RTD and the measure-
ment instrument. This mode is available for all 4-wire
configurations using internal current source excitation.
(4) Excitation Current
The next field in the channel assignment word (B17 to
B14) controls the magnitude of the excitation current
applied to the RTD (see Table 29). The current selected
is the total current flowing through the RTD independent
of the wiring configuration. The RSENSE current is 2x the
sensor excitation current for 3-wire RTDs.
In order to prevent soft or hard faults, select a current
such that the maximum voltage drop across the sensor or
sense resistor is nominally 1.0V. For example, if RSENSE
is 10kΩ and the RTD is a PT-100, select an excitation
current of 100µA for 2-wire and 4-wire RTDs and select
50µA for a 3-wire RTD. Alternatively, using a 1kΩ sense
resistor with a PT-100 RTD allows 500µA excitation for
any wiring configuration.
(5) RTD Curve
Bits B13 and B12 set the RTD curve used and the cor-
responding Callendar-Van Dusen constants (shown in
Table 30).
(6) Custom RTD Data Pointer
In the case where an RTD not listed in Table 30 is used,
a custom RTD table may be entered into the LTC2983.
See Custom RTD section near the end of this data sheet
for more information.
Table 30. RTD Curves: RT = R0 • (1 + a • T + b • T2 + (T – 100°C) • c • T3) for T < 0°C, RT = R0 • (1 + a • T + b • T2) for T > 0°C
(5) CURVE
B13 B12 CURVE ALPHA a b c
0 0 European Standard 0.00385 3.908300E-03 –5.775000E-07 –4.183000E-12
0 1 American 0.003911 3.969200E-03 –5.849500E-07 –4.232500E-12
1 0 Japanese 0.003916 3.973900E-03 –5.870000E-07 –4.400000E-12
1 1 ITS-90 0.003926 3.984800E-03 –5.870000E-07 –4.000000E-12
X X RTD1000-375 0.00375 3.810200E-03 –6.018880E-07 –6.000000E-12
X X *NI-120 N/A N/A N/A N/A
*NI-120 uses table based data.
LTC2983
L7 LJUW 3 1
LTC2983
31
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Fault Reporting – RTD
Each sensor type has unique fault reporting mechanism
indicated in the most significant byte of the data output
word. Table 31 shows faults reported in the measurement
of RTDs.
Bit D31 indicates the RTD or RSENSE is open, shorted, or not
plugged in. This is a hard fault and –999°C or °F is reported.
Bit D30 indicates a bad ADC reading. This can be a result
of either a broken (open) sensor or an excessive noise
event (ESD or static discharge into the sensor path). This
is a hard error and –999°C or °F is reported. In the case of
an excessive noise event, the device should recover and
the following conversions will be valid if the noise was a
random infrequent event. Bits D29 and D28 are not used
for RTDs. Bits D27 and D26 indicate over or under tem-
perature limits (see Table 32). The calculated temperature
is reported, but the accuracy may be compromised. Bit
D25 indicates the absolute voltage measured by the ADC
is beyond its normal operating range. If an RTD is used
as the cold junction element, any hard or soft error is also
flagged in the thermocouple result.
Table 32. Voltage and Resistance Ranges
RTD TYPE MIN Ω MAX Ω LOW TEMP LIMIT °C HIGH TEMP LIMIT °C
PT-10 1.95 34.5 –200 850
PT-50 9.75 172.5 –200 850
PT-100 19.5 345 –200 850
PT-200 39 690 –200 850
PT-500 97.5 1725 –200 850
PT-1000 195 3450 –200 850
NI-120 66.6 380.3 –80 260
Custom Table Lowest Table Entry Highest Table Entry Lowest Table Entry Highest Table Entry
Table 31. RTD Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open or Short RTD or RSENSE –999°C or °F
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F
D29 Not Used for RTDs N/A Always 0 Valid Reading
D28 Not Used for RTDs N/A Always 0 Valid Reading
D27 Sensor Over Range Soft T > High Temp Limit (See Table 32) Suspect Reading
D26 Sensor Under Range Soft T < Low Temp Limit (See Table 32) Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading
D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading
LTC2983
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Table 33. Sense Resistor Channel Assignment Word
(1) SENSOR TYPE (2) SENSE RESISTOR VALUE (Ω)
FIGURE 36 FIGURE 40
Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to ≈ 131,072Ω with 1/1024Ω Resolution
Table 34. Sense Resistor Selection
(1) SENSOR TYPE
B31 B30 B29 B28 B27 SENSOR TYPE
1 1 1 0 1 Sense Resistor
Table 35. Example Sense Resistor Values
(2) SENSE RESISTOR VALUE (Ω)
B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Example R 216 215 214 213 212 211 210 292827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10
10,000.2Ω 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 1
99.99521kΩ 1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1 1 0 0 1 1 0 1 0 1 1 1
1.0023kΩ 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 1 0 0 1 0 0 1 1 0 0 1 1
Sense Resistor
can be tied directly to 2-lead RTD elements. The disad-
vantages of this topology are errors due to parasitic lead
resistance. If sharing is not selected (1 RSENSE per RTD),
then CHRTD should be grounded. The ground connection
should be removed if sharing is enabled (1 RSENSE for
multiple RTDs).
(2) Sense Resistor Value
The last field in the channel assignment word (B26 to B0)
sets the value of the sense resistor within the range 0 to
131,072Ω with 1/1024Ω precision (see Table 35). The top
17 bits (B26 to B10) create the integer and bits B9 to B0
create the fraction of the sense resistor value.
Example: 2-Wire RTD
The simplest RTD configuration is the 2-wire configura-
tion, 2-wire RTDs follow the general convention shown in
Figure 7. They require only two connections per RTD and
Sense resistor channel assignments follow the general
convention shown in Figure 8. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHRSENSE is
tied to the 2nd terminal of the RTD. Channel assignment
data (see Table 33) is mapped into a memory location
corresponding to CHRSENSE.
Figure 7. 2-Wire RTD Channel Assignment Convention
Figure 8. Sense Resistor Channel Assignment Convention for
2-Wire RTDs
2983 F07
OPTIONAL GND, REMOVE FOR RSENSE SHARING
2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE)
2
1
CHRTD-1
CH
RTD
EXCITATION
CURRENT
FLOW = CHRTD (2≤ RTD ≤ 20)
CHANNEL
ASSIGNMENT
2983 F08
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW
= CHRSENSE (2≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
Channel Assignment
For each sense resistor tied to the LTC2983, a 32-bit
channel assignment word is programmed into a memory
location corresponding to the channel the sensor is tied
to (see Table 33). This word includes (1) sense resistor
selection and (2) sense resistor value.
(1) Sensor Type
The sense resistor is selected by setting the first 5 input
bits, B31 to B27, to 11101 (see Table 34).
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Example: 2-Wire RTDs with Shared RSENSE
Figure 9 shows a typical temperature measurement system
using multiple 2-wire RTDs. In this example, a PT-1000
RTD ties to CH17 and CH18 and an NI-120 RTD ties to
CH19 and CH20. Using this configuration, the LTC2983 can
digitize up to nine 2-wire RTDs with a single sense resistor.
RTD #1 sensor type and configuration data are as-
signed to CH18. 32 bits of binary configuration data are
mapped directly into memory locations 0x244 to 0x247
(see Table 36). RTD #2 sensor type and configuration data
are assigned to CH20. 32-bits of binary configuration data
are mapped directly into memory locations 0x24C to 0x24F
Table 36. Channel Assignment Data for 2-Wire RTD #1 (PT-1000, RSENSE on CH16, 2-Wire, Shared RSENSE, 10µA Excitation Current,
α = 0.003916 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x244
MEMORY
ADDRESS 0x245
MEMORY
ADDRESS 0x246
MEMORY
ADDRESS 0x247
(1) RTD TYPE PT-1000 5 01111 0 1 1 1 1
(2) Sense Resistor
Channel Pointer
CH16 5 10000 1 0 0 0 0
(3) Sensor
Configuration
2-Wire with
Shared RSENSE
4 0001 0 0 0 1
(4) Excitation
Current
10µA 4 0010 0 0 1 0
(5) Curve Japanese,
α = 0.003916
2 10 1 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
(see Table 37). The sense resistor is assigned to CH16.
The user-programmable value of this resistor is 5001.5Ω.
32bits of binary configuration data are mapped directly
into memory locations 0x23C to 0x23F (see Table 38).
A conversion is initiated on CH18 by writing 10010010 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01010010. The resulting temperature in
°C can be read from memory locations 0x054 to 0x057
(corresponding to CH18). A conversion can be initiated
and read from CH20 in a similar fashion.
Figure 9. Shared 2-Wire RTD Example
RSENSE
5001.5Ω
0.01µF
2983 F09
0.01µF
SENSE RESISTOR ASSIGNED TO CH16 (CHRSENSE=16)
RTD #1 ASSIGNED TO CH18 (CHRTD=18)
RTD #2 ASSIGNED TO CH20 (CHRTD=20)
CH20
CH19
CH16
CH15
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x244 TO 0x247
RESULT MEMORY LOCATIONS 0x054 TO 0x057
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x24C TO 0x24F
RESULT MEMORY LOCATIONS 0x05C TO 0x05F
0.01µF
0.01µF
CH17
CH18
0.01µF
0.01µF
2-WIRE PT-1000
2-WIRE NI-120
2
1
2
1
LTC2983
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LTC2983
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Example: 3-Wire RTD
3-wire RTD channel assignments follow the general con-
vention shown in Figure 10. Terminals 1 and 2 tie to the
input/excitation current sources and terminal 3 connects
to the sense resistor. Channel assignment data is mapped
to memory locations corresponding to CHRTD.
Table 37. Channel Assignment Data for 2-Wire RTD #2 (NI-120, RSENSE on CH16, 2-Wire, Shared RSENSE, 100µA Excitation Current)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x24C
MEMORY
ADDRESS 0x24D
MEMORY
ADDRESS 0x24E
MEMORY
ADDRESS 0x24F
(1) RTD TYPE NI-120 5 10001 1 0 0 0 1
(2) Sense Resistor
Channel Pointer
CH16 5 10000 1 0 0 0 0
(3) Sensor
Configuration
2-Wire with
Shared RSENSE
4 0001 0 0 0 1
(4) Excitation
Current
100µA 4 0101 0 1 0 1
(5) Curve European
α = 0.00385
2 00 0 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 38. Channel Assignment Data for Sense Resistor (Value = 5001.5Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
5001.5Ω 27 000010011100010011000000000 000010011100010011000000000
Sense resistor channel assignments follow the general
convention shown in Figure 11. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHRSENSE is
tied to the 3rd terminal of the RTD and CHRSENSE-1 is tied
to ground (or left floating for RSENSE sharing). Channel
assignment data (see Table 33) is mapped into the memory
location corresponding to CHRSENSE.
Figure 10. 3-Wire RTD Channel Assignment Convention Figure 11. 3-Wire Sense Resistor Channel Assignment
Convention for 3-Wire RTDs
2983 F10
3RD TERMINAL TIES TO SENSE RESISTOR
2
3
1
CHRTD-1
CHRSENSE
CH
RTD
EXCITATION
CURRENT
FLOW = CHRTD (2≤ RTD ≤ 20)
CHANNEL
ASSIGNMENT
2983 F11
CHRSENSE-1
CHRSENSE
RSENSE
2x EXCITATION
CURRENT
FLOW = CHRSENSE (2≤ RSENSE ≤ 20)
(OPTIONAL GND, REMOVE FOR RSENSE SHARING)
CHANNEL
ASSIGNMENT
LTC2983
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Table 39. Channel Assignment Data for 3-Wire RTD (PT-200, RSENSE on CH7, 3-Wire, 50µA Excitation Current, α = 0.003911 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x220
MEMORY
ADDRESS 0x221
MEMORY
ADDRESS 0x222
MEMORY
ADDRESS 0x223
(1) RTD TYPE PT-200 5 01101 0 1 1 0 1
(2) Sense
Resistor Channel
Pointer
CH75 00111 0 0 1 1 1
(3) Sensor
Configuration
3-Wire 4 0100 0 1 0 0
(4) Excitation
Current
50µA 4 0100 0 1 0 0
(5) Curve American,
α = 0.003911
2 01 0 1
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 40. Channel Assignment Data for Sense Resistor (Value = 12150.39Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x218
MEMORY
ADDRESS 0x219
MEMORY
ADDRESS 0x21A
MEMORY
ADDRESS 0x21B
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense Resistor
Value
12150.39Ω 27 000101111011101100110001111 0 0 0 1 0 1 1 1 1 0 1 1 1 0 1 1 0 0 1 1 0 0 0 1 1 1 0
APPLICATIONS INFORMATION
Figure 12 shows a typical temperature measurement sys-
tem using a 3-wire RTD. In this example, a 3-wire RTD’s
terminals tie to CH9, CH8, and CH7. The sense resistor
ties to CH7 and CH6. The sense resistor and RTD connect
together at CH7.
The 3-wire RTD reduces the errors associated with para-
sitic lead resistance by applying excitation current to each
RTD input. This first order cancellation removes matched
lead resistance errors. This cancellation does not remove
errors due to thermocouple effects or mismatched lead
resistances. The RTD sensor type and configuration data
are assigned to CH9. 32 bits of binary configuration data
are mapped directly into memory locations 0x220 to 0x223
(see Table 39). The sense resistor is assigned to CH7. The
user-programmable value of this resistor is 12150.39Ω.
32 bits of binary configuration data are mapped directly
into memory locations 0x218 to 0x21B (see Table 40).
Figure 12. 3-Wire RTD Example
RSENSE
12,150.39Ω
0.01µF
2983 F12
0.01µF
RSENSE ASSIGNED TO CH7 (CHSENSE=7)
3-WIRE RTD ASSIGNED TO CH9 (CHRTD=9)
CH7
CH6
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x218 TO 0x21B
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x220 TO 0x223
RESULT MEMORY LOCATIONS 0x030 TO 0x033
0.01µF
0.01µF
CH8
CH9
3-WIRE PT-200
2
3
1
LTC2983
36 L7ELUEN2
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A conversion is initiated on CH9 by writing 10001001 into
memory location 0x000 . Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01001001. The resulting temperature in
°C can be read from memory locations 0x030 to 0x033
(corresponding to CH9).
Example: Standard 4-Wire RTD (No Rotation or RSENSE
Sharing)
Standard 4-wire RTD channel assignments follow the
general convention shown in Figure 13. Terminal 1 is
tied to ground, terminals 2 and 3 (Kelvin sensed signal)
tie to CHRTD and CHRTD-1, and the 4th terminal ties to the
sense resistor. Channel assignment data (see Table 25)
is mapped to memory locations corresponding to CHRTD.
Sense resistor channel assignments follow the general
convention shown in Figure 14. The sense resistor is tied
between CHRSENSE and CHSENSE-1, where CHRSENSE is
tied to the 4th terminal of the RTD. Channel assignment
data (see Table 33) is mapped into a memory location
corresponding to CHRSENSE.
Figure 13. 4-Wire RTD Channel Assignment Convention
Figure 14. Sense Resistor Channel Assignment Convention for
4-Wire RTDs
2983 F13
3
4
1
2
CHRTD-1
CH
RTD
CH
RSENSE
4TH TERMINAL TIES TO SENSE RESISTOR (CH
RSENSE
)
EXCITATION
CURRENT
FLOW = CHRTD (2≤ RTD ≤ 20)
CHANNEL
ASSIGNMENT
2983 F14
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW = CHRSENSE (2≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
LTC2983
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LTC2983
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Table 41. Channel Assignment Data for 4-Wire RTD (PT-1000, RSENSE on CH11, Standard 4-Wire, 25µA Excitation Current,
α = 0.00385 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x230
MEMORY
ADDRESS 0x231
MEMORY
ADDRESS 0x232
MEMORY
ADDRESS 0x233
(1) RTD TYPE PT-1000 5 01111 0 1 1 1 1
(2) Sense
Resistor Channel
Pointer
CH11 5 01011 0 1 0 1 1
(3) Sensor
Configuration
4-Wire,
No Rotate,
No Share
4 1000 1 0 0 0
(4) Excitation
Current
25µA 4 0011 0 0 1 1
(5) Curve European,
α=0.00385
2 00 0 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 42. Channel Assignment Data for Sense Resistor (Value = 5000.2Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x228
MEMORY
ADDRESS 0x229
MEMORY
ADDRESS 0x22A
MEMORY
ADDRESS 0x22B
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
5000.2Ω 27 000010011100010000011001100 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0
Figure 15 shows a typical temperature measurement
system using a 4-wire RTD. In this example, a 4-wire
RTD’s terminals tie to GND, CH13, CH12, and CH11. The
sense resistor ties to CH11 and CH10. The sense resis-
tor and RTD share a common connection at CH11. The
RTD sensor type and configuration data are assigned to
CH13. 32 bits of binary configuration data are mapped
directly into memory locations 0x230 to 0x233 (see
Table 41). The sense resistor is assigned to CH11. The
user programmable value of this resistor is 5000.2Ω.
32 bits of binary configuration data are mapped directly
into memory locations 0x228 to 0x22B (see Table 42).
A conversion is initiated on CH13 by writing 10001101
into the data byte at memory location 0x000. Once the
conversion is complete, the INTERRUPT pin goes HIGH
and memory location 0x000 becomes 01001101. The
resulting temperature in °C can be read from memory
locations 0x040 to 0x043 (corresponding to CH13).
Figure 15. Standard 4-Wire RTD Example
RSENSE
5000.2Ω
0.01µF
2983 F15
0.01µF
SENSE RESISTOR ASSIGNED TO CH11 (CHSENSE=11)
RTD ASSIGNED TO CH13 (CHRTD=13)
CH11
CH10
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x228 TO 0x22B
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x230 TO 0x233
RESULT MEMORY LOCATIONS 0x040 TO 0x043
0.01µF
0.01µF
CH12
CH13
4-WIRE PT-1000
3
4
2
1
LTC2983
38 L7ELUEN2
LTC2983
38
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Example: 4-Wire RTD with Rotation
One method to improve the accuracy of an RTD over the
standard 4-wire implementation is by rotating the excita-
tion current source. Parasitic thermocouple effects are
automatically removed through autorotation. In order to
perform autorotation, the 1st terminal of the RTD ties to
CHRTD+1 instead of GND, as in the standard case. This
allows the LTC2983 to automatically change the direc-
tion of the current source without the need for additional
external components.
4-wire RTD with rotation channel assignments follow
the general convention shown in Figure 16. Terminal 1 is
tied to CHRTD+1, terminals 2 and 3 (Kelvin sensed signal)
tie to CHRTD and CHRTD-1, and the 4th terminal ties to the
sense resistor. Channel assignment data (see Table25) is
mapped to memory locations corresponding to CHRTD.
Sense resistor channel assignments follow the general
convention shown in Figure 17. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHRSENSE is
tied to the 4th terminal of the RTD. Channel assignment
data is mapped into a memory location corresponding to
CHRSENSE.
Figure 16. 4-Wire RTD Channel Assignment Convention
Figure 17. Sense Resistor Channel Assignment Convention for
4-Wire RTDs with Rotation
2983 F17
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW = CHRSENSE (2≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
2983 F16
3
4
1
2
CHRTD–1
CHRTD
CHRTD+1
EXCITATION
CURRENT
FLOW = CHRTD (2≤ RTD ≤ 19)
CHRSENSE 4TH TERMINAL TIES TO SENSE RESISTOR
CHANNEL
ASSIGNMENT
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Table 43. Channel Assignment Data for Rotating 4-Wire RTD (PT-100, RSENSE on CH6, Rotating 4-Wire, 100µA Excitation Current,
α = 0.003911 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) RTD TYPE PT-100 5 01100 0 1 1 0 0
(2) Sense
Resistor Channel
Pointer
CH65 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire with
Rotation
4 1010 1 0 1 0
(4) Excitation
Current
100µA 4 0101 0 1 0 1
(5) Curve American,
α=0.003911
2 01 0 1
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 44. Channel Assignment Data for Sense Resistor (Value = 10.0102kΩ)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x214
MEMORY
ADDRESS 0x215
MEMORY
ADDRESS 0x216
MEMORY
ADDRESS 0x217
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense Resistor
Value
10.0102kΩ 27 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0
APPLICATIONS INFORMATION
Figure 18 shows a typical temperature measurement
system using a rotating 4-wire RTD. In this example
a 4-wire RTD’s terminals tie to CH17, CH16, CH15,
and CH6. The sense resistor is tied to CH6 and CH5.
The sense resistor and RTD connect together at CH6.
The RTD sensor type and configuration data are as-
signed to CH16. 32 bits of binary configuration data are
mapped directly into memory locations 0x23C to 0x23F
(see Table 43). The sense resistor is assigned to CH6.
The user programmable value of this resistor is 10.0102kΩ.
32 bits of binary configuration data are mapped directly
into memory locations 0x214 to 0x217 (see Table 44).
A conversion is initiated on CH16 by writing 10010000 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01010000. The resulting temperature in
°C can be read from memory locations 0x04C to 0x04F
(corresponding to CH16).
Figure 18. Rotating 4-Wire RTD Example
RSENSE
10.0102k
0.01µF
2983 F18
0.01µF
SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6)
RTD ASSIGNED TO CH16 (CHRTD=16)
CH6
CH5
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x214 TO 0x217
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
RESULT MEMORY LOCATIONS 0x04C TO 0x04F
0.01µF
CH15
CH16
CH17
PT-100 0.01µF
0.01µF
3
4
2
1
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APPLICATIONS INFORMATION
Example: Multiple 4-Wire RTDs with Shared RSENSE
Figure 19 shows a typical temperature measurement
system using two 4-wire RTDs with a shared RSENSE.
The LTC2983 can support up to six 4-wire RTDs with
a single sense resistor. In this example, the first 4-wire
RTD’s terminals tie to CH17, CH16, CH15, and CH6 and
the 2nd ties to CH20, CH19, CH18, and CH6. The sense
resistor ties to CH5 and CH6. The sense resistor and both
RTDs connect together at CH6. This channel assignment
convention is identical to that of the rotating RTD. This
Table 45. Channel Assignment Data for 4-Wire RTD #1 (PT-100, RSENSE on CH6, 4-Wire, Shared RSENSE, Rotated 100µA Excitation
Current, α = 0.003926 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) RTD TYPE PT-100 5 01100 0 1 1 0 0
(2) Sense
Resistor Channel
Pointer
CH65 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire
Rotated
4 1010 1 0 1 0
(4) Excitation
Current
100µA 4 0101 0 1 0 1
(5) Curve ITS-90,
α=0.003926
2 11 1 1
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
topology supports both rotated and non-rotated RTD
excitations. Channel assignment data for each sensor is
shown in Tables 45 to 47.
A conversion is initiated on CH16 by writing 10010000 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01010000. The resulting temperature in
°C can be read from memory locations 0x04C to 0x04F
(corresponding to CH16). A conversion can be initiated
and read from CH19 in a similar fashion.
Figure 19. Shared RSENSE 4-Wire RTD Example
RSENSE
10k
0.01µF
2983 F19
0.01µF
SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6)
RTD #1 ASSIGNED TO CH16 (CHRTD=16)
CH6
CH5
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x214 TO 0x217
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
RESULT MEMORY LOCATIONS 0x04C TO 0x04F
0.01µF
CH15
CH16
CH17
CH18
CH19
CH20
RTD #2 ASSIGNED TO CH19 (CHRTD=19)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x248 TO 0x24B
RESULT MEMORY LOCATIONS 0x058 TO 0x05B
4-WIRE PT-100 0.01µF
0.01µF
3
4
2
1
0.01µF
4-WIRE PT-500 0.01µF
0.01µF
3
4
2
1
LTC2983
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APPLICATIONS INFORMATION
Table 46. Channel Assignment Data for 4-Wire RTD #2 (PT-500, RSENSE on CH6, 4-Wire, Rotated 50µA Excitation Current,
α = 0.003911 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x248
MEMORY
ADDRESS 0x249
MEMORY
ADDRESS 0x24A
MEMORY
ADDRESS 0x24B
(1) RTD TYPE PT-500 5 01110 0 1 1 1 0
(2) Sense
Resistor Channel
Pointer
CH65 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire
Shared,
No Rotation
4 1001 1 0 0 1
(4) Excitation
Current
50µA 4 0100 0 1 0 0
(5) Curve American,
α=0.003911
2 01 0 1
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 47. Channel Assignment Data for Sense Resistor (Value = 10.000kΩ)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x214
MEMORY
ADDRESS 0x215
MEMORY
ADDRESS 0x216
MEMORY
ADDRESS 0x217
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
10.000kΩ 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Example: 4-Wire RTD with Kelvin RSENSE
It is possible to cancel the parasitic lead resistance in
the sense resistors by configuring the 4-wire RTD with
a 4-wire (Kelvin connected) sense resistor. This is useful
when using a PT-10 or PT-50 with a small valued RSENSE
or when the sense resistor is remotely located or in ap-
plications requiring extreme precision.
The 4-wire RTD channel assignments follow the general
conventions previously defined (Figures 14 and 16) for
a standard 4-wire RTD. The sense resistor follows the
convention shown in Figure 20.
Figure 20. Sense Resistor with Kelvin Connections Channel Assignment Convention
2983 F20
3
4
1
2
CHRSENSE–1
CHRSENSE–2
CHRSENSE
RSENSE
TIES TO RTD TERMINAL 4
EXCITATION
CURRENT
FLOW = CHRSENSE (3≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
LTC2983
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Table 48. Channel Assignment Data for 4-Wire RTD with Kelvin Connected RSENSE (PT-10, RSENSE on CH6, 4-Wire, Kelvin RSENSE with
Rotated 1mA Excitation Current, α = 0.003916 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) RTD TYPE PT-10 5 01010 0 1 0 1 0
(2) Sense Resistor
Channel Pointer
CH65 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire Kelvin RSENSE
and Rotation
4 1110 1 1 1 0
(4) Excitation Current 1mA 4 1000 1 0 0 0
(5) Curve Japanese, α=0.003916 2 10 1 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Figure 21 shows a typical temperature measurement system
using a 4-wire RTD with a Kelvin connected RSENSE. In this
example, the 4-wire RTD’s terminals tie to CH17, CH16, CH15,
and CH6. The sense resistor ties to CH6, CH5, and CH4 and
excitation current is applied to CH4 and CH17. The sense
resistor’s nominal value is 1kΩ in order to accommodate a
1mA excitation current. The sense resistor and RTD connect
together at CH6. This topology supports both rotated, shared
and standard 4-wire RTD topologies. If rotated or shared
configuration are not used then terminal 1 of the RTD is tied to
ground instead of CH17, freeing up one input channel. Channel
assignment data is shown in Tables 48 and 49.
A conversion is initiated on CH16 by writing 10010000
into memory location 0x000. Once the conver-
sion is complete, the INTERRUPT pin goes HIGH
and memory location 0x000 becomes 01010000
(see Table 6). The resulting temperature in °C can be read from
memory locations 0x04C to 0x04F (corresponding to CH16).
APPLICATIONS INFORMATION
Figure 21. Sense Resistor with Kelvin Connections Example
2983 F21
SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6)
CH4
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x214 TO 0x217
0.01µF
CH5
CH6
CH15
CH16
CH17
RTD ASSIGNED TO CH16 (CHRTD=16)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
RESULTS MEMORY LOCATIONS 0x04C TO 0x04F
RSENSE
1k
0.01µF
0.01µF
3
4
2
1
0.01µF
4-WIRE PT-10 0.01µF
0.01µF
3
4
2
1
Table 49. Channel Assignment Data for Sense Resistor (Value = 1000Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x214
MEMORY
ADDRESS 0x215
MEMORY
ADDRESS 0x216
MEMORY
ADDRESS 0x217
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
1000Ω 27 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
LTC2983
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LTC2983
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Table 50. Thermistor Channel Assignment Word
(1) THERMISTOR
TYPE
(2) SENSE RESISTOR
CHANNEL POINTER
(3) SENSOR
CONFIGURATION
(4) EXCITATION
CURRENT
(5) CUSTOM THERMISTOR
DATA POINTER
TABLE 51 TABLE 27 TABLE 52 TABLE 53 TABLES 76, 77, 78, 80, 81
Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Thermistor Type = 19 to 27 RSENSE Channel
Pointer [4:0]
SGL = 1
DIFF = 0
Excitation
Mode
Excitation Current
[3:0]
Not Used
0 0 0
Custom Address
[5:0]
Custom Length – 1
[5:0]
Table 51. Thermistor Type: 1/T=A+B•ln(R)+C•ln(R)2 + D•ln(R)3 + E•ln(R)4 + F•ln(R)5
B31 B30 B29 B28 B27 THERMISTOR TYPE A B C D E F
1 0 0 1 1 Thermistor 44004/44033
2.252kΩ at 25°C
1.46800E-03 2.38300E-04 0 1.00700E-07 0 0
1 0 1 0 0 Thermistor 44005/44030
3kΩ at 25°C
1.40300E-03 2.37300E-04 0 9.82700E-08 0 0
1 0 1 0 1 Thermistor 44007/44034
5kΩ at 25°C
1.28500E-03 2.36200E-04 0 9.28500E-08 0 0
1 0 1 1 0 Thermistor 44006/44031
10kΩ at 25°C
1.03200E-03 2.38700E-04 0 1.58000E-07 0 0
1 0 1 1 1 Thermistor 44008/44032
30kΩ at 25°C
9.37600E-04 2.20800E-04 0 1.27600E-07 0 0
1 1 0 0 0 Thermistor YSI-400
2.252kΩ at 25°C
1.47134E-03 2.37624E-04 0 1.05034E-07 0 0
1 1 0 0 1 Spectrum 1003k 1kΩ
at 25°C
1.445904E-3 2.68399E-04 0 1.64066E-07 0 0
1 1 0 1 0 Thermistor Custom
Steinhart-Hart
user input user input user input user input user input user input
1 1 0 1 1 Thermistor Custom Table not used not used not used not used not used not used
THERMISTOR MEASUREMENTS
Channel Assignment – Thermistor
For each thermistor tied to the LTC2983, a 32-bit channel
assignment word is programmed into a memory location
corresponding to the channel the sensor is tied to (see
Table 50). This data includes (1) thermistor type, (2)
sense resistor channel pointer, (3) sensor configuration,
(4) excitation current, (5) Steinhart-Hart address pointer
or custom table address pointer.
APPLICATIONS INFORMATION
(1) Thermistor Type
The thermistor type is determined by the first five input
bits (B31 to B27) as shown in Table 51. Linearization coef-
ficients based on Steinhart-Hart equation for commonly
used Thermistor types 44004/44033, 44005/44030,
44006/44031, 44007/44034, 44008/44032 and YSI-400
are built into the device. If other custom thermistors are
used, Thermistor Custom Steinhart-Hart or Thermis-
tor Custom Table (temperature vs resistance) can be
selected. In this case, user specific data can be stored
in the on-chip RAM starting at the address defined in
Thermistor Custom Steinhart-Hart or Thermistor Custom
Table address pointers.
LTC2983
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LTC2983
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Table 52. Sensor Configuration Data
(3) SENSOR
CONFIGURATION
SGL EXCITATION
MODE
SINGLE-ENDED/
DIFFERENTIAL
SHARE
RSENSE
ROTATE
B21 B20 B19
0 0 0 Differential No No
0 0 1 Differential Yes Yes
0 1 0 Differential Yes No
0 1 1 Reserved
1 0 0 Single-Ended No No
1 0 1 Reserved
1 1 0 Reserved
1 1 1 Reserved
APPLICATIONS INFORMATION
(2) Sense Resistor Channel Pointer
Thermistor measurements are performed ratiometrically
relative to a known RSENSE resistor. The sense resistor
channel pointer field indicates the differential channel
the sense resistor is tied to for the current thermistor
(see Table 27).
(3) Sensor Configuration
The sensor configuration field is used to define various
thermistor properties. Configuration bit B21 is set high
for single-ended (measurement relative to COM) and low
for differential (see Table 52).
The next sensor configuration bits (B19 and B20) deter-
mine the excitation current mode. These bits are used to
enable RSENSE sharing, where one sense resistor is used
for multiple thermistors. In this case, the thermistor ground
connection is internal and each thermistor points to the
same RSENSE channel.
Bits B19 and B20 are also used to enable excitation current
rotation to automatically remove parasitic thermocouple
effects. Parasitic thermocouple effects may arise from
the physical connection between the thermistor and the
measurement instrument. This mode is available for dif-
ferential thermistor configurations using internal current
source excitation.
(4) Excitation Current
The next field in the channel assignment word (B18 to B15)
controls the magnitude of the excitation current applied to
the thermistor (see Table 53). In order to prevent hard or
soft faults, select a current such that the maximum volt-
age drop across the sensor or sense resistor is nominally
1.0V. The LTC2983 has no special requirements related
to the ratio between the voltage drop across the sense
resistor and the sensor. Consequently, it is possible to
have a sense resistor several orders of magnitude smaller
than the maximum sensor value. For optimal performance
over the full thermistor temperature range, auto ranged
current can be selected. In this case, the LTC2983 conver-
sion is performed in three cycles (instead of the standard
two cycles) (see Table 64). The first cycle determines the
optimal excitation current for the sensor resistance value
and RSENSE value. The following two cycles use that cur-
rent to measure the thermistor temperature.
Table 53. Excitation Current for Thermistors
(4) EXCITATION CURRENT
B18 B17 B16 B15 CURRENT
0 0 0 0 Reserved
0 0 0 1 250nA
0 0 1 0 500nA
0 0 1 1 1µA
0 1 0 0 5μA
0 1 0 1 10μA
0 1 1 0 25μA
0 1 1 1 50μA
1 0 0 0 100µA
1 0 0 1 250µA
1 0 1 0 500µA
1 0 1 1 1mA
1 1 0 0 Auto Range*
1 1 0 1 Invalid
1 1 1 0 Invalid
1 1 1 1 Reserved
*Auto Range not allowed for custom sensors
(5) Steinhart-Hart Address/Custom Table Address
See Custom Thermistors section near the end of this data
sheet for more information.
LTC2983
L7HEJWEGR 45
LTC2983
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APPLICATIONS INFORMATION
Fault Reporting – Thermistor
Each sensor type has unique fault reporting mechanism in-
dicated in the upper byte of the data output word. Table 54
shows faults reported during the measurement of
thermistors.
Bit D31 indicates the thermistor or RSENSE is open, shorted,
or not plugged in. This is a hard fault and –999°C is re-
ported. Bit D30 indicates a bad ADC reading. This could be
a result of either a broken (open) sensor or an excessive
noise event (ESD or static discharge into the sensor path).
This is a hard error and –999°C is output. In the case of
an excessive noise event, the device should recover and
the following conversions will be valid if the noise event
was a random infrequent event. Bits D29 and D28 are not
used for thermistors. Bits D27 and D26 indicate the read-
ing is over or under temperature limits (see Table 55). The
calculated temperature is reported, but the accuracy may
be compromised. Bit D25 indicates the absolute voltage
measured by the ADC is beyond its normal operating range.
If a thermistor is used as the cold junction element, any
hard or soft error is flagged in the thermocouple result.
Table 54. Thermistor Fault Reporting
BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT
D31 Sensor Hard Fault Hard Open or Short Thermistor or RSENSE –999°C
D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C
D29 Not Used for Thermistors N/A Always 0 Valid Reading
D28 Not Used for Thermistors N/A Always 0 Valid Reading
D27 Sensor Over Range* Soft T > High Temp Limit Suspect Reading
D26 Sensor Under Range* Soft T < Low Temp Limit Suspect Reading
D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading
D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading
*Do not apply to custom Steinhart-Hart sensor type. Custom table thermistor over/under range is determined by the resistor table values, see custom
thermistor table example for details.
LTC2983
11
LTC2983
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Example: Single-Ended Thermistor
The simplest thermistor configuration is the single-ended
configuration. Thermistors using this configuration share
a common ground (COM) between all sensors and are
each tied to a unique sense resistor (RSENSE sharing is
not allowed for single-ended thermistors). Single-ended
thermistors follow the convention shown in Figure 22.
Terminal 1 ties to ground (COM) and terminal 2 ties to
CHTHERM and the sense resistor. Channel assignment
data (see Table 50) is mapped to memory locations cor-
responding to CHTHERM.
APPLICATIONS INFORMATION
Sense resistor channel assignments follow the general
convention shown in Figure 23. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied
to the 2nd terminal of the thermistor. Channel assignment
data (see Table 33) is mapped into the memory location
corresponding to CHRSENSE.
Table 55. Thermistor Temperature/Resistance Range
THERMISTOR TYPE MIN (Ω) MAX (Ω) LOW Temp Limit (°C) HIGH Temp Limit (°C)
Thermistor 44004/44033 2.252kΩ at 25°C 41.9 75.79k –40 150
Thermistor 44005/44030 3kΩ at 25°C 55.6 101.0k –40 150
Thermistor 44007/44034 5kΩ at 25°C 92.7 168.3k –40 150
Thermistor 44006/44031 10kΩ at 25°C 237.0 239.8k –40 150
Thermistor 44008/44032 30kΩ at 25°C 550.2 884.6k –40 150
Thermistor YSI 400 2.252kΩ at 25°C 6.4 1.66M –80 250
Spectrum 1003K 1kΩ at 25°C 51.1 39.51k –50 125
Thermistor Custom Steinhart-Hart N/A N/A N/A N/A
Thermistor Custom Table Second Table Entry Last Table Entry
Figure 22. Single-Ended Thermistor Channel Assignment
Convention
Figure 23. Sense Resistor Channel Assignment Convention
2983 F22
2
1
CHTHERM
COM
EXCITATION
CURRENT
FLOW
= CHTHERM (1 ≤ THERM ≤ 20)
2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE)
CHANNEL
ASSIGNMENT
2983 F23
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW = CHRSENSE (2≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
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APPLICATIONS INFORMATION
Figure 24 shows a typical temperature measurement
system using a single-ended thermistor. In this example
a 10kΩ (44031 type) thermistor is tied to a 10.1kΩ sense
resistor. The thermistor is assigned channel CH5 (memory
locations 0x210 to 0x213) and the sense resistor to CH4
(memory locations 0x20C to 0x20F). Channel assignment
data are shown in Tables 56 and 57.
A conversion is initiated on CH5 by writing 10000101 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01000101. The resulting temperature in
°C can be read from memory locations 0x020 to 0x023
(corresponding to CH5).
Table 56. Channel Assignment Data for Single-Ended Thermistor (44006/44031 10kΩ at 25°C Type Thermistor, Single-Ended
Configuration, RSENSE on CH4, 1µA Excitation Current)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x210
MEMORY
ADDRESS 0x211
MEMORY
ADDRESS 0x212
MEMORY
ADDRESS 0x213
(1) Thermistor
Type
44006/44031
10kΩ at 25°C
5 10110 1 0 1 1 0
(2) Sense
Resistor Channel
Pointer
CH45 00100 0 0 1 0 0
(3) Sensor
Configuration
Single-Ended 3 100 1 0 0
(4) Excitation
Current
1µA 4 0011 0 0 1 1
Not Used Set These Bits
to 0
3000 000
(5) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 57. Channel Assignment Data for Sense Resistor (Value = 10.1kΩ)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x20C
MEMORY
ADDRESS 0x20D
MEMORY
ADDRESS 0x20E
MEMORY
ADDRESS 0x20F
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
10.1kΩ 27 000100111011101000000000000 0 0 0 1 0 0 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Figure 24. Single-Ended Thermistor Example
2983 F24
SENSE RESISTOR ASSIGNED TO CH4 (CHSENSE=4)
CH3
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x20C TO 0x20F
CH4
CH5
COM
THERMISTOR ASSIGNED TO CH5 (CHTHERM=5)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x210 TO 0x213
RESULT MEMORY LOCATIONS 0x020 TO 0x023
RSENSE
10.1k
100pF
100pF
TYPE 44031
100pF
2
1
LTC2983
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LTC2983
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Example: Differential Thermistor
The differential thermistor configuration allows separate
ground sensing for each sensor. In this standard differ-
ential configuration, one sense resistor is used for each
thermistor. Differential thermistors follow the convention
shown in Figure 25. Terminal 1 ties to CHTHERM and is
shorted to ground and terminal 2 ties CHTHERM-1 to and
the sense resistor. Channel assignment data (see Table 50)
is mapped to memory locations corresponding to CHTHERM.
Sense resistor channel assignments follow the general
convention shown in Figure 26. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHRSENSE is
tied to the 2nd terminal of the thermistor. Channel as-
signment data (see Table 33) is mapped into a memory
location corresponding to CHRSENSE.
APPLICATIONS INFORMATION
Figure 25. Differential Thermistor Channel Assignment
Convention
Figure 26. Sense Resistor Channel Assignment Convention
2983 F25
2
1CHTHERM
CHTHERM–1
EXCITATION
CURRENT
FLOW = CHTHERM (2 ≤ THERM ≤ 20)
2ND TERMINAL TIES TO SENSE RESISTOR
1ST TERMINAL TIES TO GND
CHANNEL
ASSIGNMENT
2983 F26
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW = CHRSENSE (2 ≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
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Table 58. Channel Assignment Data for Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential
Configuration, RSENSE on CH11, Auto Range Excitation)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x230
MEMORY
ADDRESS 0x231
MEMORY
ADDRESS 0x232
MEMORY
ADDRESS 0x233
(1) Thermistor
Type
44008/44032
30kΩ at 25°C
5 10111 1 0 1 1 1
(2) Sense
Resistor Channel
Pointer
CH11 5 01011 0 1 0 1 1
(3) Sensor
Configuration
Differential,
No Share,
No Rotate
3 000 0 0 0
(4) Excitation
Current
Auto Range 4 1100 1 1 0 0
Not Used Set These Bits
to 0
2 000 0 0 0
(5) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 59. Channel Assignment Data for Sense Resistor (Value = 9.99kΩ)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x228
MEMORY
ADDRESS 0x229
MEMORY
ADDRESS 0x22A
MEMORY
ADDRESS 0x22B
(1) Sensor Type Sense
Resistor
5 11101 1 1 1 0 1
(2) Sense
Resistor Value
9.99kΩ 27 000100111000001100000000000 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0
APPLICATIONS INFORMATION
Figure 27 shows a typical temperature measurement
system using a differential thermistor. In this example a
30kΩ (44032 type) thermistor is tied to a 9.99kΩ sense
resistor. The thermistor is assigned channel CH13 (memory
locations 0x230 to 0x233) and the sense resistor to CH11
(memory locations 0x228 to 0x22B). Channel assignment
data is shown in Tables 58 and 59).
A conversion is initiated on CH13 by writing 10001101 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01001101. The resulting temperature in
°C can be read from memory locations 0x040 to 0x043
(Corresponding to CH13).
Figure 27. Differential Thermistor Example
2983 F27
SENSE RESISTOR ASSIGNED TO CH11 (CHSENSE=11)
CH10
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x228 TO 0x22B
CH11
CH12
CH13
THERMISTOR ASSIGNED TO CH5 (CHTHERM=13)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x230 TO 0x233
RESULT MEMORY LOCATIONS 0x040 TO 0x043
RSENSE
9.99k
100pF
100pF
TYPE 44032 100pF
2
1
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APPLICATIONS INFORMATION
Example: Shared/Rotated Differential Thermistor
The differential thermistor configuration allows separate
internal ground sensing for each sensor. In this configura-
tion, one sense resistor can be used for multiple thermis-
tors. Differential thermistors follow the convention shown
in Figure 28. Terminal 1 ties to CHTHERM and terminal 2
ties to CHTHERM-1 and the sense resistor. Channel assign-
ment data (see Table 50) is mapped to memory locations
corresponding to CHTHERM.
Sense resistor channel assignments follow the general
convention shown in Figure 29. The sense resistor is tied
between CHRSENSE and CHRSENSE-1, where CHSENSE is tied
to the 2nd terminal of the thermistor. Channel assignment
data (see Table 33) is mapped into a memory location
corresponding to CHTHERM.
Figure 30 shows a typical temperature measurement
system using a shared sense resistor and one rotated/
one non-rotated differential thermistors. In this example
Figure 28. Thermistor with Shared RSENSE Channel
Assignment Convention
Figure 29. Sense Resistor Channel Assignment
Convention for Thermistors
2983 F28
2
1
CHTHERM–1
CHTHERM
EXCITATION
CURRENT
FLOW = CHTHERM (2 ≤ THERM ≤ 20)
2ND TERMINAL TIES TO SENSE RESISTOR
CHANNEL
ASSIGNMENT 2983 F29
CHRSENSE-1
CHRSENSE
RSENSE
EXCITATION
CURRENT
FLOW = CHRSENSE (2 ≤ RSENSE ≤ 20)
CHANNEL
ASSIGNMENT
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Table 60. Channel Assignment Data Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential Configuration with
Sharing and Rotation, RSENSE on CH16, 250nA Excitation Current)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x244
MEMORY
ADDRESS 0x245
MEMORY
ADDRESS 0x246
MEMORY
ADDRESS 0x247
(1) Thermistor
Type
44008/44032
30kΩ at 25°C
5 10111 1 0 1 1 1
(2) Sense
Resistor Channel
Pointer
CH16 5 10000 1 0 0 0 0
(3) Sensor
Configuration
Differential,
Rotate and
Shared
3 001 0 0 1
(4) Excitation
Current
250nA
Excitation
Current
4 0001 0 0 0 1
Not Used Set These Bits
to 0
3 000 0 0 0
(5) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
APPLICATIONS INFORMATION
a 30kΩ (44032 Type) thermistor is tied to a 10.0kΩ sense
resistor and configured as rotated/shared. The second
thermistor a 2.25kΩ (44004 Type) is configured as a
non-rotated/shared. Channel assignment data are shown
in Tables 60 to 62.
A conversion is initiated on CH18 by writing 10010010 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01010010. The resulting temperature in
°C can be read from memory locations 0x054 to 0x057
(corresponding to CH16). A conversion can be initiated
and read from CH20 in a similar fashion.
Figure 30. Rotated and Shared Thermistor Example
2983 F30
THERMISTOR #1 ASSIGNED TO CH18 (CHTHERM=18)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x244 TO 0x247
RESULT MEMORY LOCATIONS 0x054 TO 0x057
100pF
CH17
CH16
CH15
CH18
CH19
CH20
THERMISTOR #2 ASSIGNED TO CH20 (CHTHERM=20)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x24C TO 0x24F
RESULT MEMORY LOCATIONS 0x05C TO 0x05F
SENSE RESISTOR ASSIGNED TO CH16 (CHSENSE=16)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
TYPE 44032
RSENSE
10k
100pF
2
1
100pF
TYPE 44033 100pF
2
1
100pF
100pF
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Table 62. Channel Assignment Data for Sense Resistor (Value = 10.0kΩ)
Configuration
Field
Description # Bits Binary Data MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
10.0kΩ 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Table 61. Channel Assignment Data Differential Thermistor (44004/44033 2.252kΩ at 25°C Type Thermistor, Differential
Configuration with Sharing and No Rotation, RSENSE on CH16, 10µA Excitation Current)
Configuration
Field
Description # Bits Binary Data MEMORY
ADDRESS 0x24C
MEMORY
ADDRESS 0x24D
MEMORY
ADDRESS 0x24E
MEMORY
ADDRESS 0x24F
(1) Thermistor
Type
44004/44033
2.252kΩ at
25°C
5 10011 1 0 0 1 1
(2) Sense
Resistor Channel
Pointer
CH16 5 10000 1 0 0 0 0
(3) Sensor
Configuration
Differential,
No Rotate
and Shared
3 010 0 1 0
(4) Excitation
Current
10µA
Excitation
Current
4 0101 0 1 0 1
Not Used Set These
Bits to 0
3 000 0 0 0
(5) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
APPLICATIONS INFORMATION
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APPLICATIONS INFORMATION
Typical Application Thermocouple Measurements
The LTC2983 includes 20 fully configurable analog input
channels. Each input channel can be configured to accept
any sensor type. Figure 31 shows a typical application
digitizing multiple thermocouples. Each thermocouple
requires a cold junction sensor and each cold junction
sensor can be shared amongst multiple thermocouples.
For example, the thermocouple tied to CH1 can use the
diode tied to CH2 as a cold junction sensor. However, any
thermocouple (CH1, CH3, CH5, CH6, CH9, CH10, or CH16)
can use any diode (CH2, CH4, or CH7), RTD (CH13, CH14),
or Thermistor (CH19, CH20) as its cold junction compen-
sation. The LTC2983 simultaneously measures both the
thermocouple and cold junction sensor and outputs the
results in °C or °F.
Figure 31. Typical Thermocouple Application
CH2
CH3
CH4
CH5
CH6
CH7
CH8
CH9
CH11
CH12
CH13
CH14
CH15
CH10
CH1 VDD
Q1
Q2
Q3
CS
SDI
SDO
SCK
VREFOUT
VREFP
16
48
47
46
13
14
11
43
42
41
40
39
38
37
2, 4, 6, 8, 45
2.85V TO 5.25V
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
2983 F31
CH16
CH17
CH18
CH19
CH20
COM
0.1µF
10µF
10µF
1µF
VREF_BYP
1µF
LDO
10µF
(OPTIONAL, DRIVE
LOW TO RESET)
SPI INTERFACE
1, 3, 5, 7, 9, 12, 15, 44
RESET
INTERRUPT
GND
RSENSE
RSENSE
4-WIRE
RTD
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APPLICATIONS INFORMATION
Typical Application RTD and Thermistor Measurements
The LTC2983 includes 20 fully configurable analog input
channels. Each input channel can be configured to accept
any sensor type. Figure 32 shows a typical application
digitizing multiple RTDs and thermistors. Each RTD/
thermistor requires a sense resistor which can be shared
with multiple sensors. RTDs can be configured as 2, 3,
or 4-wire topologies. For example, a single sense resistor
(CH1, CH2) is shared between a 4-wire RTD (CH4, CH3), a
2-wire RTD (CH7, CH6), two 3-wire RTDs (CH9, CH8 and
CH11, CH10) and a thermistor (CH13, CH12). This can
be mixed with diode sensors (CH15) and thermocouples
(CH14). Sense resistors (CH17, CH16) can also be dedi-
cated to specific sensors, in this case a 4-wire RTD (CH19,
CH18). Current is applied through both the sense resistor
and RTD/Thermistor, the resulting voltages are simulta-
neously measured and the results are output in °C or °F.
Figure 32. Typical RTD/Thermistor Application
CH2
CH3
CH4
CH5
CH6
CH7
CH8
CH9
CH11
CH12
CH13
CH14
CH15
CH10
CH1
Q1
Q2
Q3
VDD
RSENSE
RSENSE
CS
SDI
SDO
SCK
VREFOUT
VREFP
16
48
47
46
13
14
11
43
42
41
40
39
38
37
2, 4, 6, 8, 45
2.85V TO 5.25V
17
4-WIRE
RTD
2-WIRE
RTD
3-WIRE
RTD
3-WIRE
RTD
4-WIRE
RTD
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
2983 F32
CH16
CH17
CH18
CH19
CH20
COM
0.1µF
10µF
10µF
1µF
VREF_BYP
1µF
LDO
10µF
(OPTIONAL, DRIVE
LOW TO RESET)
SPI INTERFACE
1, 3, 5, 7, 9, 12, 15, 44
RESET
INTERRUPT
GND
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SUPPLEMENTAL INFORMATION
2983 F33
CHADC
SINGLE-ENDED CHANNEL
ASSIGNMENT = CHADC (1 ≤ ADC ≤ 20)
= CHADC (2 ≤ ADC ≤ 20)
24-BIT
∆∑ ADC
24-BIT
∆∑ ADC CHANNEL
ASSIGNMENT
DIFFERENTIAL
COM
CHADC
CHADC-1
–
+
–
+
Figure 33. Direct ADC Channel Assignment Conventions
Table 63. Direct ADC Output Format
START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3
(END ADDRESS)
D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Fault Data SIGN MSB LSB
Volts Sensor
Hard
Fault
Range
Hard
Fault
NA NA Soft
Above
Soft
Below
Soft
Range
Valid
Always
1 ± 2V 1V 0.5V 0.25V ...
Integer Fraction
>VREF 1 1 0 0 1 0 1 CLAMPED to Factory Programmed Value
of VREF
1.75 • VREF/2 1 1 0 0 1 0 1 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1.125 • VREF/2 0 0 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
VREF/2 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
VREF/222 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–VREF/222 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
–VREF/2 0 0 0 0 0 0 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–1.125 • VREF 0 0 0 0 0 1 1 1 1 1 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
–1.75 • VREF 1 1 0 0 0 1 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
< –VREF 1 1 0 0 0 1 1 1 CLAMPED to Factory Programmed Value
of –VREF
Direct ADC Measurements
In addition to measuring temperature sensors, the LTC2983
can perform direct voltage measurements. Any channel
can be configured to perform direct single-ended or dif-
ferential measurements. Direct ADC channel assignments
follow the general convention shown in Figure 33. The
32-bit channel assignment word is programmed into a
memory location corresponding to the input channel.
The channel assignment word is 0xF000 0000 for differ-
ential readings and 0xF400 0000 for single-ended. The
positive input channel ties to CHADC for both single-ended
and differential modes. For single-ended measurements
the ADC negative input is COM while for differential mea-
surements it is CHADC-1. For single ended measurements,
COM can be driven with any voltage above GND–50mV
and below VDD–0.3V.
The direct ADC results are available in memory at a
location corresponding to the conversion channel.
LTC2983
LTC2983
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SUPPLEMENTAL INFORMATION
The data is represented as a 32-bit word (see Table 63)
where the eight most significant bits are fault bits and the
bottom 24 are the ADC reading in volts. For direct ADC
readings hard fault errors do not clamp the digital output.
Readings beyond ±1.125 • VREF/2 exceed the normal ac-
curacy range of the LTC2983 and flag a soft error; these
results should be discarded. Readings beyond ±1.75 •
VREF/2 exceed the usable range of the LTC2983; these
result in a hard fault and should be discarded.
Figures 34 to 36 show typical integral nonlinearity varia-
tion at various supply voltages and temperatures for a
differential input voltage (±VREF/2) and VREF/2 common
mode input voltage.
Figure 34. Integral Nonlinearity as a Function of
Temperature at VDD = 5.25V
Figure 36. Integral Nonlinearity as a Function of
Temperature at VDD = 2.85V
Figure 35. Integral Nonlinearity as a Function of
Temperature at VDD = 3.3V
DIFFERENTIAL INPUT VOLTAGE (V)
INL ERROR (ppm)
2983 F34
20
15
10
5
0
–5
–10
–15
–20
–1.5 –0.5 0 0.5 1 1.5–1
90°C
25°C
–45°C
DIFFERENTIAL INPUT VOLTAGE (V)
INL ERROR (ppm)
2983 F35
20
15
10
5
0
–5
–10
–15
–20
–1.5 –0.5 0 0.5 1 1.5–1
90°C
25°C
–45°C
DIFFERENTIAL INPUT VOLTAGE (V)
INL ERROR (ppm)
2983 F36
20
15
10
5
0
–5
–10
–15
–20
–1.5 –0.5 0 0.5 1 1.5–1
90°C
25°C
–45°C
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SUPPLEMENTAL INFORMATION
Table 64. 2- and 3-Cycles Conversion Modes
TYPE OF SENSOR CONFIGURATION NUMBER OF
CONVERSION
CYCLES
MAXIMUM OUTPUT
TIME
Thermocouple OC = 0 2 167.2ms
RTD All 2 167.2ms
Thermistor Non-Autorange
Current
2 167.2ms
Diode Two Readings 2 167.2ms
Thermocouple OC = 1 3 251ms
Thermocouple OC = 0, 3-Cycle
Cold Junction
3 251ms
Thermistor Autorange
Current
3 251ms
Diode Three Readings 3 251ms
Fault Protection and Anti-Aliasing
The LTC2983 analog input channels draw a maximum
of 1nA DC. As a result, it is possible to add anti-aliasing
and fault protection circuitry directly to the input of the
LTC2983. The most common input circuitry is a low pass
filter with 1k to 10k resistance (limited by excitation current
for RTDs and thermistors) and a capacitor with 100pF-0.1µf
capacitance. This circuit can be placed directly between
the thermocouples and 4-wire RTDs and the LTC2983.
In the case of 3-wire RTDs, mismatch errors between
the protection resistors can degrade the performance.
Thermistors requiring input projection should be tied to
the LTC2983 through a Kelvin type connection in order to
avoid errors due to the fault protection resistors.
2- and 3-Cycle Conversion Modes
The LTC2983 performs multiple internal conversions in
order to determine the sensor temperature. Normally, two
internal conversion cycles are required for each tempera-
ture result providing a maximum output time of 167.2ms.
The LTC2983 uses these two cycles to automatically
remove offset/offset drift errors, reduce 1/f noise, auto-
calibrate matched internal current sources, and provide
simultaneous 50/60Hz noise rejection.
In addition to performing two conversion cycles per result,
the LTC2983 also offers several unique features by utilizing
a 3rd conversion cycle. In this case, the maximum output
time is 251ms and all the benefits of the 2-cycle modes
are present (see Table 64).
One feature utilizing the three conversion cycle mode is the
internal open circuit detect mode. Typically, thermocouple
open circuit detection is performed by adding a high re-
sistance pull-up between the thermocouple and VDD. This
method can be used with the LTC2983 while operating
in the two conversion cycle mode (OC=0). This external
pull-up can interact with the input protection circuitry and
lead to temperature measurement errors and increased
noise. These problems are eliminated by selecting the
internal open circuit detection mode (OC=1). In this case,
a current is pulsed for 8ms and allowed to settle during
one conversion cycle. This is followed by the normal two
conversion cycle measurement of the thermocouple. If
the thermocouple is broken, the current pulse will result
in an open circuit fault.
A second feature taking advantage of the 3rd conversion
cycle is thermistor excitation current auto ranging. Since
a thermistor’s resistance varies many orders of magni-
tude, the performance in the low resistance regions are
compromised by the small currents required by the high
resistance regions of operation. The auto ranging mode
applies a test current during the first conversion cycle in
order to determine the optimum current for the resistance
state of the thermistor. It then uses that current to perform
the thermistor measurement using the normal 2-cycle
measurement. If a 3-cycle thermistor measurement is used
as the cold junction sensor for a 2-cycle thermocouple
measurement, the thermocouple conversion result is
ready after three cycles.
A third feature requiring a 3rd conversion cycle is the
three current diode measurement. In this mode, three
ratioed currents are applied to the external diode in order
to cancel parasitic lead resistance effects. This is useful
in applications where the diode is remotely located and
significant, unknown parasitic lead resistance requires
cancellation. If a 3-cycle diode or thermistor measure-
ment is used as the cold junction sensor for a 2-cycle
thermocouple measurement, the thermocouple conversion
result is ready after three cycles.
LTC2983
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Table 65. Multiple Conversion Mask Register
MEMORY LOCATION B7 B6 B5 B4 B3 B2 B1 B0
0x0F4 Reserved
0x0F5 CH20 CH19 CH18 CH17
0x0F6 CH16 CH15 CH14 CH13 CH12 CH11 CH10 CH9
0x0F7 CH8 CH7 CH6 CH5 CH4 CH3 CH2 CH1
Table 66. Example Mask Register Select CH20, CH19, CH16, and CH1
MEMORY LOCATION B7 B6 B5 B4 B3 B2 B1 B0
0x0F4 Reserved
0x0F5 1 1 0 0
0x0F6 1 0 0 0 0 0 0 0
0x0F7 0 0 0 0 0 0 0 1
SUPPLEMENTAL INFORMATION
Running Conversions Consecutively on Multiple
Channels
Generally, during the Initiate Conversion state, a conver-
sion measurement is started on a single input chan-
nel determined by the channel number (bits B[4:0] =
00001 to 10100) written into memory location 0x000.
Multiple consecutive conversions can be initiated by writing
bits B[4:0]=00000 into memory location 0. Conversions
will be initiated on each channel selected in the mask
register (see Table 65).
For example, using the mask data shown in Table 66, after
1000000 is written into memory location 0, conversions
are initiated consecutively on CH20, CH19, CH16, and CH1.
Once the conversions begin, the INTERRUPT pin goes LOW
and remains LOW until all conversions are complete. If
the mask register is set for a channel that has no assign-
ment data, that conversion step is skipped. All the results
are stored in the conversion result memory locations and
can be read at the conclusion of the measurement cycle.
Entering/Exiting Sleep Mode
The LTC2983 can be placed into sleep mode by writing
0x97 to memory location 0x000. On the rising edge of
CS following the memory write (see Figure 2) the device
enters the low power sleep state. It remains in this state
until CS is brought low or RESET is asserted. Once one
of these two signals is asserted, the LTC2983 begins its
start-up cycle as described in State 1: Start-Up section
of this data sheet.
MUX Configuration Delay
The LTC2983 performs 2 or 3 internal conversion cycles
per temperature result. Each conversion cycle is performed
with different excitation and input multiplexer configura-
tions. Prior to each conversion, these excitation circuits
and input switch configurations are changed and an
internal 1ms (typical) delay ensures settling prior to the
conversion cycle in most cases.
LTC2983
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SUPPLEMENTAL INFORMATION
If excessive RC time constants are present in external
sensor circuits (large bypass capacitors used for thermis-
tors or RTDs) it is possible to increase the settling time
between current source excitation and MUX switching.
The extra delay is determined by the value written into
the MUX configuration delay register (memory location
0x0FF). The value written into this memory location is
multiplied by 100µs; therefore the maximum extra MUX
delay is 25.5ms (i.e. 0x0FF = 255 • 100µs).
Global Configuration Register
The LTC2983 includes a global configuration register
(memory location 0x0F0, see Figure 37). This register is
used to set the notch frequency of the digital filter and
temperature results format (°C or °F). The default setting is
simultaneous 50/60Hz rejection (75dB rejection with 1ms
MUX delay). If higher 60Hz rejection is required (120dB
rejection), write 0x01 into memory location 0x0F0; if higher
50Hz rejection is required (120dB rejection) write 0x02
into memory location 0x0F0.
In addition to digitizing standard thermocouples, the
LTC2983 can also digitize user-programmable, custom
thermocouples (thermocouple type=0b01001, see Table
12). Custom sensor data (minimum of three, maximum of
64 pairs) reside sequentially in memory and are arranged
in blocks of six bytes of monotonically increasing tabular
data as mV vs temperature (see Table 67).
Table 67. Custom Thermocouple Tabular Data Format
ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5
0x250 + 6* Start Address Table Entry #1 (mV) Table Entry #1 (Kelvin)
0x250 + 6* Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Kelvin)
0x250 + 6* Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Kelvin)
• • •
• • •
• • •
Max Address = 0x3CA Table Entry #64 (mV) Table Entry #64 (Kelvin)
Figure 37. Global Configuration Register
2983 F37
0 = °C
1 = °F
00 50/60Hz REJECTION
01 60Hz REJECTION
10 50Hz REJECTION
11 RESERVED
MEMORY LOCATION 0x0F0 0 0 0 0 0
}
The default temperature units reported by the LTC2983
are °C. The reported temperature can also be output in °F
by setting bit 3 of memory location 0x0F0 to 1. All other
global configuration bits should be set to 0.
Reference Considerations
The mechanical stress of soldering the LTC2983 to a PC
board can cause the output voltage reference to shift and
temperature coefficient to change. These two changes are
not correlated. For example, the voltage may shift but the
temperature coefficient may not. To reduce the effects of
stress-related shifts, mount the reference near the short
edge of the PC board or in a corner.
Figure 38. Custom Thermocouple Example (mV vs Kelvin)
2983 F38
TEMPERATURE (K)
p9
p8
p7
p6
p5
p4
p3
(0mV, 0K)
NOTE:
P0 SHOULD BE THE
EXTRAPOLATION
POINT TO 0K
VOLTAGE (mV)
p2
p1
p0
VOLTAGE < p1
SOFT FAULT
CONDITION
VOLTAGE > p9
SOFT FAULT
CONDITION
(0mV, 273.15K)
CUSTOM THERMOCOUPLES
Custom Thermocouple Example
In this example, a simplified thermocouple curve is
implemented (see Figure 38). Points P1 to P9 represent
the normal operating range of the custom thermocouple.
Voltage readings above point P9 result in a soft fault and
the reported temperature is a linear extrapolation using
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a slope determined by points P8 and P9 (the final two
table entries). Voltage readings below point P1 are also
reported as soft faults. The temperature reported is the
extrapolation between point P1 and P0, where P0 is typi-
cally the sensor output voltage at 0 Kelvin. If P0 is above
0 Kelvin, then all sensor output voltages below P0 (in mV)
will report 0 Kelvin.
CUSTOM THERMOCOUPLES
In order to program the LTC2983 with the custom ther-
mocouple table, both the mV data and the Kelvin data are
converted to 24-bit binary values (represented as two 3-byte
table entries). Since most thermocouples generate negative
output voltages, the mV values input to the LTC2983 are
2’s compliment. The sensor output voltage (units=mV),
follows the convention shown in Table 69, where the first
bit is the sign, the next nine are the integer part and the
remaining 14 bits are the fractional part.
Table 68. Thermocouple Example mV vs Kelvin (K) Data Memory Map
POINT SENSOR OUTPUT
VOLTAGE (mV)
TEMPERATURE
KELVIN
START
ADDRESS
STOP
ADDRESS
BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5
P0 –50.22 0 0x250 0x255
P1 –30.2 99.1 0x256 0x25B
P2 –5.3 135.4 0x25C 0x261
P3 0 273.15 0x262 0x267
P4 40.2 361.2 0x268 0x26D mV Data Temperature Data
P5 55.3 522.1 0x26E 0x273 (see Table 69) (see Table 70)
P6 88.3 720.3 0x274 0x279
P7 132.2 811.2 0x27A 0x27F
P8 188.7 922.5 0x280 0x285
P9 460.4 1000 0x286 0x28B
Table 69. Example Thermocouple Output Voltage Values (mV)
BYTE 0 BYTE 1 BYTE 2
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
mV Sign 2827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 2–11 2–12 2–13 2–14
–50.22 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0
–30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 0 0
–5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0
55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1
88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1
132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0
188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0
460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1
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CUSTOM THERMOCOUPLES
In order to simplify the temperature field, temperature
values are input in Kelvin as an unsigned value, but the
final temperatures reported by the LTC2983 are reported
in °C or °F. The sensor temperature (Kelvin), follows the
convention shown in Table 70, where the first 14 bits
are the integer part and the remaining 10 bits are the
fractional part.
In this example, a custom thermocouple tied to CH1, with
a cold junction sensor on CH2, is programmed with the
channel assignment data shown in Table 71 (refer to Figure
6 for similar format). In this case the custom data begins at
memory location 0x250 (starting address is 0). The start-
ing address (offset from 0x250) is entered in the custom
thermocouple data pointer field of the channel assignment
data. The table data length –1 (9 in this example) is entered
into the custom thermocouple data length field of the
thermocouple channel assignment word. Refer to Table 68
where the number of six byte entries is 10.
Table 70. Example Thermocouple Temperature Values
BYTE 3 BYTE 4 BYTE 5
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Temperature 213 212 211 210 292827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 0
135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1
273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1
361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0
522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0
720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1
811.2 0 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0
922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0
1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
Table 71. Custom Thermocouple Channel Assignment Data
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY
DATA
MEMORY
ADDRESS 200
MEMORY
ADDRESS 201
MEMORY
ADDRESS 202
MEMORY
ADDRESS 203
(1) Thermocouple
Type
Type Custom 5 01001 0 1 0 0 1
(2) Cold Junction
Channel Pointer
CH25 00010 0 0 0 1 0
(3) Sensor
Configuration
Single-Ended,
10µA Open Circuit
4 1100 1 1 0 0
Not Used Set These Bits to 0 6 000000 0 0 0 0 0 0
(4) Custom
Thermocouple Data
Pointer
Start Address = 0
(Start at 0x250)
6 000000 0 0 0 0 0 0
Custom
Thermocouple Data
Length-1
Data Length –1
= 9
(10 Paired Entries)
6 001010 0 0 1 0 0 1
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In addition to digitizing standard RTDs, the LTC2983
can also digitize custom RTDs (RTD type=0b10010, see
Table26). Custom sensor data (minimum of three, maxi-
mum of 64 pairs) reside sequentially in memory and are
arranged in blocks of six bytes of monotonically increasing
tabular data Ω vs temperature (see Table 72).
Table 72. Custom RTD/Thermistor Tabular Data Format
ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5
0x250 + 6* Start Address Table Entry #1 (Ω) Table Entry #1 (Kelvin)
0x250 + 6* Start Address + 6 Table Entry #2 (Ω) Table Entry #2 (Kelvin)
0x250 + 6* Start Address + 12 Table Entry #3 (Ω) Table Entry #3 (Kelvin)
• • •
• • •
• • •
Max Address = 0x3CA Table Entry #64 (Ω) Table Entry #64 (Kelvin)
CUSTOM RTDS
Custom RTD Example
In this example, a simplified RTD curve is implemented (see
Figure 39). Points P1 to P9 represent the normal operating
range of the custom RTD. Resistance readings above point
P9 result in a soft fault and the reported temperature is
a linear extrapolation using a slope determined by points
P8 and P9 (the final two table entries). Resistance read-
ings below point P1 are also reported as soft faults. The
temperature reported is the extrapolation between point
P1 and P0, where P0 is the sensor output temperature
at 0Ω (This point should be 0Ω for proper interpolation
below point p1).
Figure 39. Custom RTD Example (Ω vs Kelvin )
2983 F39
p9
p8
p7
p6
p5
p4
p3
NOTE:
P0 SHOULD BE THE
EXTRAPOLATION
POINT TO 0Ω
RESISTANCE (Ω)
TEMPERATURE (K)
p2
p1
0
0p0
RESISTANCE < p1
SOFT FAULT
CONDITION
RESISTANCE > p9
SOFT FAULT
CONDITION
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Custom RTD table data is formatted in Ω (sensor output
resistance) vs Kelvin (see Table 73). Each table entry pair
spans six bytes. The first set of data can begin at any
memory location greater than or equal to 0x250 and end
at or below 0x3CF.
In order to program the LTC2983 with the custom RTD
table, both the resistance data and the Kelvin data are
converted to 24-bit binary values. The sensor output
CUSTOM RTDS
resistance (units=Ω) follows the convention shown in
Table 74, where the first 13 bits are the integer part and
the remaining 11 bits are the fractional part.
In order to simplify the temperature field, temperature
values are input in Kelvin as an unsigned value, but the
final temperatures reported by the LTC2983 are reported
in °C or °F. The sensor temperature (Kelvin) follows the
Table 73. RTD Example Resistance vs Kelvin Data Memory Map
POINT SENSOR OUTPUT
RESISTANCE (Ω)
TEMPERATURE
(K)
START
ADDRESS
STOP
ADDRESS
BYTE 1 BYTE 2 BYTE 3 BYTE 1 BYTE 2 BYTE 3
P0 0 112.3 0x28C 0x291
P1 80 200.56 0x292 0x297
P2 150 273.16 0x298 0x29D
P3 257.36 377.25 0x29E 0x2A3
P4 339.22 489.66 0x2A4 0x2A9 Resistance Data Temperature Data
P5 388.26 595.22 0x2AA 0x2AF
P6 512.99 697.87 0x2B0 0x2B5
P7 662.3 765.14 0x2B6 0x2BB
P8 743.5 801.22 0x2BC 0x2C1
P9 2001.89 900.5 0x2C2 0x2C7
Table 74. Example RTD Resistance Values
BYTE 1 BYTE 2 BYTE 3
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Resistance 212 211 210 292827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 2–11
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
80 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
150 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0
257.36 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 1 1 0 0 0 0 1
339.22 0 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 0
388.26 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0
512.99 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 0 1 1
662.3 0 0 0 1 0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0
743.5 0 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0
2001.89 0 0 1 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0
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convention shown in Table 75, where the first 14 bits
are the integer part and the remaining 10 bits are the
fractional part.
In this example, a custom RTD tied to CH12/13, with a
sense resistor on CH10/11, is programmed with the chan-
nel assignment data shown in Table 76 (refer to Figure 15
for a similar format). In this case, the custom data begins
at memory location 0x28C (starting address is 10). The
starting address (offset from 0x250) is entered in the
custom RTD data pointer field of the channel assignment
data. The table data length –1 (9 in this case) is entered
into the custom RTD data length field of the channel as-
signment word. Refer to Table 72 where the total number
of paired entries is 10.
Table 75. Example RTD Temperature Values
BYTE 1 BYTE 2 BYTE 3
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Temperature 213 212 211 210 292827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10
112.3 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1
200.56 0 0 0 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 1
273.16 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 1 1
377.25 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0
489.66 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1
595.22 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1
697.87 0 0 0 0 1 0 1 0 1 1 1 0 0 1 1 1 0 1 1 1 1 0 1 0
765.14 0 0 0 0 1 1 0 1 1 1 1 1 0 1 0 0 1 0 0 0 1 1 1 1
801.22 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 1
900.5 0 0 0 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0
Table 76. Custom RTD Channel Assignment Data
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY
DATA
MEMORY
ADDRESS 230
MEMORY
ADDRESS 231
MEMORY
ADDRESS 232
MEMORY
ADDRESS 233
(1) RTD Type Custom 5 10010 1 0 0 1 0
(2) Sense Resistor
Channel Pointer
CH11 5 01011 0 1 0 1 1
(3) Sensor
Configuration
4-Wire, No
Rotate, No Share
4 1000 1 0 0 0
(4) Excitation Current 25µA 4 0011 0 0 1 1
(5) Curve Not Used for
Custom
2 00 0 0
(6) Custom RTD Data
Pointer
Start Address
= 10
6 001010 0 0 1 0 1 0
(6) Custom RTD Data
Length-1
Data Length –1
= 9
10 Paired Entries
6 001001 0 0 1 0 0 1
CUSTOM RTDS
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CUSTOM THERMISTORS
In addition to digitizing standard thermistors, the
LTC2983 can also digitize custom thermistors (thermistor
type=0b11011, see Table 51). Custom sensor data (mini-
mum of three, maximum of 64 pairs) reside sequentially
in memory and are arranged in blocks of six bytes of
monotonically increasing tabular data Ω vs temperature
(see Table 72).
Custom Thermistor Table Example
In this example, a simplified thermistor NTC (negative tem-
perature coefficient) curve is implemented (see Figure 40).
Points P1 to P9 represent the normal operating range of
the custom thermistor. Resistance readings above point
P9 result in a soft fault and the reported temperature is
a linear extrapolation using a slope determined by points
P8 and P9 (the final two table entries). Resistance read-
ings below point P1 are also reported as soft faults. The
temperature reported is the extrapolation between point
P1 and P0, where P0 is the sensor output temperature
at 0Ω (This point must be 0Ω for proper interpolation
below point p1).
In addition to NTC type thermistors, it is also possible to
implement PTC (positive temperature coefficient) type
thermistors (see Figure 41). In both cases, table entries
start at the minimum resistance and end at the maximum
resistance value.
Figure 40. Custom NTC Thermistor Example (Ω vs Kelvin)
Figure 41. Custom PTC Thermistor Example (Ω vs Kelvin)
2983 F40
p9
p8
p7
p6
p5
p4
p3
NOTE:
P0 SHOULD BE THE
EXTRAPOLATION
POINT TO 0Ω
RESISTANCE (Ω)
TEMPERATURE (K)
p2
p1
0
0
p0
RESISTANCE < p1
SENSOR UNDER-RANGE
SOFT FAULT CONDITION
RESISTANCE > p9
SENSOR OVER-RANGE
SOFT FAULT CONDITION
2983 F41
p9
p8
p7
p6
p5
p4
p3
NOTE:
P0 SHOULD BE THE
EXTRAPOLATION
POINT TO 0Ω
RESISTANCE (Ω)
TEMPERATURE (K)
p2
p1
0
0p0
RESISTANCE < p1
SENSOR UNDER-RANGE
SOFT FAULT CONDITION
RESISTANCE > p9
SENSOR OVER-RANGE
SOFT FAULT CONDITION
LTC2983
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Custom thermistor table data is formatted in Ω (sensor
output resistance) vs Kelvin (see Table 77). Each table
entry pair spans six bytes. The first set of data can begin
at any memory location greater than or equal to 0x250
and end below 0x3CF.
In order to program the LTC2983 with the custom therm-
istor table, both the resistance data and the Kelvin data
are converted to 24-bit binary values. The sensor output
resistance (units=Ω) follows the convention shown in
CUSTOM THERMISTORS
Table 77. NTC Thermistor Example Resistance vs Kelvin Data Memory Map
POINT SENSOR OUTPUT
RESISTANCE(Ω)
TEMPERATURE
(K)
START
ADDRESS
STOP
ADDRESS
BYTE 1 BYTE 2 BYTE 3 BYTE 1 BYTE 2 BYTE 3
P0 0 457.5 0x2C8 0x2CD
P1 80 400.2 0x2CE 0x2D3
P2 184 372.3 0x2D4 0x2D9
P3 423.2 320.1 0x2DA 0x2DF
P4 973.36 290.55 0x2E0 0x2E5 Resistance Data Temperature Data
P5 2238.728 249.32 0x2E6 0x2EB
P6 5149.0744 240.3 0x2EC 0x2F1
P7 26775.18688 230 0x2F2 0x2F7
P8 139230.9718 215.3 0x2F8 0x2FD
P9 724001.0532 200 0x2FE 0x303
Table 78, where the first 20 bits are the integer part and
the remaining four bits are the fractional part.
In order to simplify the temperature field, temperature
values are input in Kelvin as an unsigned value, but the
final temperatures reported by the LTC2983 are reported
in °C or °F. The sensor temperature (Kelvin) follows the
convention shown in Table 79, where the first 14 bits
are the integer part and the remaining 10 bits are the
fractional part.
Table 78. Example Thermistor Resistance Values
BYTE 1 BYTE 2 BYTE 3
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Resistance 219 218 217 216 215 214 213 212 211 210 292827262524232221202–1 2–2 2–3 2–4
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
80 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0
184 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0
423.2 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 1
973.36 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1
2238.728 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 1 1 1 0 1 0 1 1
5149.074 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 1
26775.19 0 0 0 0 0 1 1 0 1 0 0 0 1 0 0 1 0 1 1 1 0 0 1 1
139231 0 0 1 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 0 0
724001.1 1 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1
LTC2983
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Table 79. Example Thermistor Temperature Values
BYTE 1 BYTE 2 BYTE 3
B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Temperature 213 212 211 210 292827262524232221202–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10
457.5 0 0 0 0 0 1 1 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0
400.2 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0
372.3 0 0 0 0 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 1 0 0 1 1
320.1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0
290.55 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 0 1 1
249.32 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1
240.3 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1
230 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0
215.3 0 0 0 0 0 0 1 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1
200 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
CUSTOM THERMISTORS
Table 80. Custom Thermistor Channel Assignment Data
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY
DATA
MEMORY
ADDRESS 210
MEMORY
ADDRESS 211
MEMORY
ADDRESS 212
MEMORY
ADDRESS 213
(1) Thermistor Type Custom Table 5 11011 1 1 0 1 1
(2) Sense Resistor
Channel Pointer
CH45 00100 0 0 1 0 0
(3) Sensor
Configuration
Single-Ended 3 100 1 0 0
(4) Excitation Current 1µA 4 0011 0 0 1 1
Not Used Set These Bits
to 0
3 00 0 0 0
(5) Custom Thermistor
Data Pointer
Start Address
= 20
6 010100 0 1 0 1 0 0
(5) Custom Thermistor
Length-1
Length –1 = 9 6 001001 0 0 1 0 0 1
In this example, a custom thermistor tied to CH5, with a
sense resistor on CH3/4, is programmed with the channel
assignment data shown in Table 80 (refer to Figure 24
for similar format). In this case the custom data begins
at memory location 0x2C8 (starting address is 20). The
starting address (offset from 0x250) is entered in the
custom thermistor data pointer field of the channel as-
signment data. The table data length –1 (9 in this case)
is entered into the custom thermistor data length field of
the thermistor channel assignment word.
LTC2983
68 L7ELUEN2
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In addition to custom table driven thermistors, it is also
possible to directly input Steinhart-Hart coefficients into
the LTC2983 (thermistor type 11010, see Table 51).
Steinhart-Hart coefficients are commonly specified
parameters provided by thermistor manufacturers. The
Steinhart-Hart equation is:
1
T= A+B•ln(R)+C•ln(R)2+D•ln(R)3+E•ln(R)4
+F •ln(R)
5
CUSTOM THERMISTORS
Steinhart-Hart data is stored sequentially in any memory
location greater than or equal to 0x250 and below 0x3CF.
Each coefficient is represented by a standard, single-
precision, IEEE754 32-bit value (see Table 81).
Example Custom Steinhart-Hart Thermistor
In this example a Steinhart-Hart equation is entered into
memory starting at location 0x300 (see Table 82).
Table 81. Steinhart-Hart Custom Thermistor Data Format
ADDRESS COEFFICIENT VALUE
0x250 + 4 *Start Address A 32-Bit Single-Precision Floating Point Format
0x250 + 4 *Start Address + 4 B 32-Bit Single-Precision Floating Point Format
0x250 + 4 *Start Address + 8 C 32-Bit Single-Precision Floating Point Format
0x250 + 4 *Start Address + 12 D 32-Bit Single-Precision Floating Point Format
0x250 + 4 *Start Address + 16 E 32-Bit Single-Precision Floating Point Format
0x250 + 4 *Start Address + 20 F 32-Bit Single-Precision Floating Point Format
Table 82. Custom Steinhart-Hart Data Example
COEFFICIENT VALUE START
ADDRESS
SIGN EXPONENT MANTISSA
MSB LSB MSB LSB
A 1.45E-03 0x300 0 0 1 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1
B 2.68E-04 0x304 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 1 1 0 1 0
C 0 0x308 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D 1.64E-07 0x30C 0 0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 0 1 0
E 0 0x310 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
F 0 0x314 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
LTC2983
L7HDN§QB 69
LTC2983
69
2983fc
For more information www.linear.com/LTC2983
A custom thermistor tied to CH5, with a sense resistor on
CH3/4, is programmed with the channel assignment data
shown in Table 83 (refer to Figure 24 for a similar format).
In this case the custom data begins at memory location
0x26E (starting address is 30). The starting address
(offset from 0x250) is entered in the custom thermistor
data pointer field of the channel assignment data. The data
length (set to 0) is always six 32-bit floating point words.
Universal Sensor Hardware
The LTC2983 can be configured as a universal temperature
measurement device. Up to four sets of universal inputs
can be applied to a single LTC2983. Each of these sets can
directly digitize a 3-wire RTD, 4-Wire RTD, Thermistor, or
thermocouple without changing any on board hardware
(see Figure 42). Each sensor can share the same four ADC
inputs and protection/filtering circuitry are configured us-
ing software changes (new channel assignment data) only.
One sense resistor and cold junction sensor are shared
among all four banks of sensors.
CUSTOM THERMISTORS
The LTC2983 includes many flexible, software configurable
input modes. In order to share four common inputs among
all four sensor types each sensor requires specific con-
figuration bits (see Table 84). 3-Wire RTDs are configured
with shared RSENSE, 4-Wire RTDs and thermistors are
configured as shared and/or rotated, thermocouples are
configured differential with internal ground, and diodes
are configured as single-ended.
Table 83. Custom Steinhart-Hart Channel Assignment Data
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY
DATA
MEMORY
ADDRESS 210
MEMORY
ADDRESS 211
MEMORY
ADDRESS 212
MEMORY
ADDRESS 213
(1) Thermistor Type Custom
Steinhart-Hart
5 11010 1 1 0 1 0
(2) Sense Resistor
Channel Pointer
CH45 00100 0 0 1 0 0
(3) Sensor
Configuration
Single-Ended 3 100 1 0 0
(4) Excitation Current 1µA 4 0011 0 0 1 1
Not Used Set These Bits
to 0
3 00 0 0 0
(5) Custom Thermistor
Data Pointer
Start Address
= 30
6 011110 0 1 1 1 1 0
(5) Custom Steinhart-
Hart Length Always
Set to 0
Fixed at Six
32-Bit Words
6 000000 0 0 0 0 0 0
Table 84. Sensor Configuration for Universal Hookup
SENSOR TYPE CONFIGURATION
OPTIONS
CONFIGURATION
BITS
SEE TABLE
3-WIRE RTD Share B18 = 1, B19 = 0 Table 28
4-WIRE RTD Share B18 = 1, B19 = 0 Table 28
4-WIRE RTD Rotate B18 = 0, B19 = 1 Table 28
Thermistor Share B19 = 0, B20 = 1 Table 52
Thermistor Rotate B19 = 1, B20 = 0 Table 52
Thermocouple Single-Ended B21 = 1 Table 14
Diode Single-Ended B26 = 1 Table 17
LTC2983
7O L7ELUEN2
LTC2983
70
2983fc
For more information www.linear.com/LTC2983
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC2938#packaging for the most recent package drawings.
LX48 LQFP 0113 REV A
0° – 7°
11° – 13°
0.45 – 0.75
1.00 REF
11° – 13°
9.00 BSC
A A
7.00 BSC
1
2
7.00 BSC
9.00 BSC
48
1.60
MAX
1.35 – 1.45
0.05 – 0.150.09 – 0.20 0.50
BSC 0.17 – 0.27
GAUGE PLANE
0.25
NOTE:
1. PACKAGE DIMENSIONS CONFORM TO JEDEC #MS-026 PACKAGE OUTLINE
2. DIMENSIONS ARE IN MILLIMETERS
3. DIMENSIONS OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.25mm ON ANY SIDE, IF PRESENT
4. PIN-1 INDENTIFIER IS A MOLDED INDENTATION, 0.50mm DIAMETER
5. DRAWING IS NOT TO SCALE
SEE NOTE: 4
C0.30 – 0.50
R0.08 – 0.20
7.15 – 7.25
5.50 REF
1
2
5.50 REF
7.15 – 7.25
48
PACKAGE OUTLINE
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
SECTION A – A
0.50 BSC
0.20 – 0.30
1.30 MIN
LX Package
48-Lead Plastic LQFP (7mm × 7mm)
(Reference LTC DWG # 05-08-1760 Rev A)
e3
LTCXXXX
LX-ES
Q_ _ _ _ _ _
XXYY
TRAY PIN 1
BEVEL PACKAGE IN TRAY LOADING ORIENTATION
COMPONENT
PIN “A1”
LTC2983
L7 LJUW 7 1
LTC2983
71
2983fc
For more information www.linear.com/LTC2983
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 07/15 Removed Tape and Reel options
Added Absolute Maximum Ratings for Q1, Q2, Q3, LDO, VREFOUT, VREF_BYP
Changed reference Output Voltage Temperature Coefficient
Changed Error Contribution for thermocouples
Changed filter capacitor values in Figures 9, 12, 15, 18, 19, 21
3
3
4
13
33, 35, 37, 39,
40, 42
B 09/15 Revised Table 2A. Memory Map
Revised the following tables so that all bytes contain eight bits: Table 69, 70, 74, 75, 78, 79
14
60, 61, 63, 64,
66, 67
C 01/16 Added H-Grade option 3, 4
LTC2983
J lz-IHfi-IHJ-IHim-IHIJ WM»
L7LJCUEN2
LTC2983
72
2983fc
For more information www.linear.com/LTC2983
LINEAR TECHNOLOGY CORPORATION 2014
LT 0116 REV C• PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC2983
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TYPICAL APPLICATION
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Reference
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Monitors Temperature and Two Voltages, Adjustable Thresholds, Open Drain Alert Outputs,
Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy
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Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy
LTC2997 Remote/Internal Temperature Sensor Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy
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Battery Chemistry and Capacity
Figure 42. Universal Inputs Allow Common Hardware Sharing for Thermocouples, Diodes,
Thermistors, 3-Wire RTDs, and 4-Wire RTDs
2983 F42
1
4
RSENSE
THERMISTOR
THERMOCOUPLE 3-WIRE RTD 4-WIRE RTD
SHARE WITH ALL
FOUR SETS OF SENSORS
2
3
3
1
1
2
2CH3
CH2
CH1
0.1µF
10µF
10µF
2.85V TO 5.25V
LTC2983
CH4
CH5
CH6
42
36
21
20
19
18
17 48
47
46
13
14
11
43