ADM8845 Datasheet by Analog Devices Inc.

ANALOG DEVICES
Charge Pump Driver for LCD
White LED Backlights
Data Sheet ADM8845
Rev. D Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©2004–2018 Analog Devices, Inc. All rights reserved.
Technical Support www.analog.com
FEATURES
Drives 6 LEDs from 2.6 V to 5.5 V (Li-Ion) input supply
1×/1.5×/2× fractional charge pump to maximize power
efficiency
1% maximum LED current matching
Up to 88% power efficiency over Li-Ion range
Powers main and sub display LEDs with individual shutdown
Package footprint only 9 mm2 (3 mm × 3 mm)
Package height only 0.75 mm
Low power shutdown mode
Shutdown function
Soft-start limiting in-rush current
APPLICATIONS
Cellular phones with main and sub displays
White LED backlighting
Camera flash/strobes and movie lights
Micro TFT color displays
DSC
PDAs
GENERAL DESCRIPTION
The ADM8845 uses charge pump technology to provide the
power required to drive up to six LEDs. The LEDs are used for
backlighting a color LCD display, having regulated constant
current for uniform brightness intensity. The main display can
have up to four LEDs, and the sub display can have one or two
LEDs. The digital CTRL1 and CTRL2 input control pins control
the shutdown operation and the brightness of the main and sub
displays.
To maximize power efficiency, the charge pump can operate in
a 1×, 1.5×, or 2× mode. The charge pump automatically
switches between 1×/1.5×/2× modes, based on the input voltage,
to maintain sufficient drive for the LED anodes at the highest
power efficiency.
Improved brightness matching of the LEDs is achieved by a
feedback pin to sense individual LED current with a maximum
matching accuracy of 1%.
FUNCTIONAL BLOCK DIAGRAM
CURRENT
CONTROL 1
CURRENT
CONTROL 2
CURRENT
CONTROL 3
CURRENT
CONTROL 4
CURRENT
CONTROL 5
CURRENT
CONTROL 6
CONTROL
LOGIC V
REF
CHARGE PUMP
1/1.5/2 MODE
OSC
LED
CURRENT
CONTROL
CIRCUIT
FB1
CURRENT CONTROLLED SINKS
FB2
FB3
FB4
FB5
FB6
V
OUT
C4
4.7F
V
CC
C1
1F
CTRL1
CTRL2
C2
1F
R
SET
I
SET
GND
C3
2.2F
ADM8845
04867-0-001
MAIN SUB
Figure 1.
ADM8845 Data Sheet
Rev. D | Page 2 of 18
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 4
Thermal Resistance ...................................................................... 4
ESD Caution .................................................................................. 4
Pin Configuration and Function Descriptions ............................. 5
Typical Performance Characteristics ............................................. 6
Theory of Operation ...................................................................... 10
Output Current Capability ........................................................ 11
Automatic Gain Control ............................................................ 11
Current Matching ....................................................................... 11
Brightness Control with a Digital PWM Signal ..................... 11
LED Brightness Control Using a PWM Signal Applied to
VPWM ............................................................................................. 13
LED Brightness Control Using a DC Voltage Applied to
VBRIGHT .......................................................................................... 13
Applications Information .............................................................. 14
Layout Considerations and Noise ............................................ 14
White LED Shorting .................................................................. 14
Driving Fewer than Six LEDs ................................................... 14
Driving Flash LEDs .................................................................... 15
Driving Camera Light, Main, and Sub LEDs.......................... 15
Driving Four Backlight White LEDs and Flash LEDs ........... 16
Power Efficiency ......................................................................... 17
Outline Dimensions ....................................................................... 18
Ordering Guide .......................................................................... 18
REVISION HISTORY
5/2018—Rev. C to Rev. D
Changes to Features Section............................................................ 1
Add Thermal Resistance Section .................................................... 4
Changes to Figure 2 .......................................................................... 5
Updated Outline Dimensions ....................................................... 18
Changes to Ordering Guide .......................................................... 18
1/2011—Rev. B to Rev. C
Changes to Figure 18 and Figure 19 ............................................... 8
Changes to Ordering Guide .......................................................... 18
4/2010—Rev. A to Rev. B
Changes to Figure 2 .......................................................................... 5
Changes to Figure 4 .......................................................................... 6
Changes to Figure 16 to Figure 19 ................................................... 8
Changes to Brightness Control with a Digital PWM Signal
Section .............................................................................................. 11
Added Exposed Pad Notation to Outline Dimensions ............. 18
Changes to Ordering Guide .......................................................... 18
7/2005—Rev. 0 to Rev. A
Changes to Table 3 ............................................................................. 5
Changes to Table 7 .......................................................................... 12
Updated Outline Dimensions ....................................................... 18
Changes to Ordering Guide .......................................................... 18
10/2004—Revision 0: Initial Version
Data Sheet ADM8845
Rev. D | Page 3 of 18
SPECIFICATIONS
VCC = 2.6 V to 5.5 V, TA = −40°C to +85°C, unless otherwise noted. C1, C2 = 1.0 µF, C3 = 2.2 µF, and C4 = 4.7 µF.
Table 1.
Parameter Min Typ Max Unit Test Conditions
INPUT VOLTAGE, VCC 2.6 5.5 V
SUPPLY CURRENT, ICC 2.6 5 mA All six LEDs disabled, VCC = 3.3 V, RSET = 7.08 kΩ, CTRL1 = 1, CRTL2 =
1
SHUTDOWN CURRENT 5 µA
CHARGE PUMP FREQUENCY 1.5 MHz
CHARGE PUMP MODE THRESHOLDS
1.5× to 2× 3.33 V
Accuracy 4 %
2× to 1.5× 3.36 V
Accuracy 4 %
Hysteresis 40 mV
1× to 1.5× 4.77 V
Accuracy 4 %
1.5× to 1× 4.81 V
Accuracy 4 %
Hysteresis 40 mV
ISET PIN
LED
LED Matching −1 +1 % ILED = 20 mA, VFB =0.4 V
ISET Accuracy −1 +1 % ILED = 20 mA, RSET = 7.08 kΩ, VFB = 0.4 V, VCC = 3.6 V, TA = 25°C
ISET Pin Voltage 1.18 V
ILED to ISET Ratio 120
MIN COMPLIANCE ON FBx PIN 0.2 0.3 V ISET = 20 mA
Charge Pump Output Resistance 1.2 1.8 Ω 1× mode
3.5 5.1 Ω 1.5× mode
8.0 14 Ω 2× mode
LED Current 30 mA Guaranteed by design. Not 100% production tested. See Figure 21.
PWM 0.1 200 kHz
DIGITAL INPUTS
Input High 0.5 VCC V
Input Low 0.3 VCC V
Input Leakage Current 1 µA
CHARGE PUMP POWER EFFICIENCY 88 % CTRL1 = 1, CRTL2 = 1, VCC = 3.4 V, VFB = 0.2 V, IFB = 20 mA
VOUT RIPPLE 30 mV VCC = 3.6 V, ILED = 20 mA, all six LEDs enabled
Am ESD (elenvoslaki: discharge) sensitive deviKe. Chavged devlces and own buavds can dwxchavge wlthnul daemon Although ans pmdm featuves palemed m pmpHeuvy pmeman (Immvy, damage may cum on dewces summed m mgh energy ESD Thevemve, pmpev ESD pveiaunons momd be Iaken m avoid pevfovmame degvadanon m ‘05: of fundionamy.
ADM8845 Data Sheet
Rev. D | Page 4 of 18
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 2.
Parameter Rating
Supply Voltage, VCC −0.3 V to +6.0 V
ISET −0.3 V to +2.0 V
CTRL1, CTRL2 −0.3 V to +6.0 V
VOUT Shorted1 Indefinite
Feedback Pins FB1 to FB6 −0.3 V to +6.0 V
Operating Temperature Range
Six LEDs Enabled with 30 mA/LED2 −40°C to +65°C
Six LEDs Enabled with 20 mA/LED2 −40°C to +85°C
VOUT3 180 mA
Storage Temperature Range −65°C to +125°C
Power Dissipation 2 mW
Electrostatic Discharge (ESD) Class 1
1 Short through LED.
2 LED current should be derated above TA > 65°C, refer to Figure 21.
3 Based on long-term current density limitations.
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
THERMAL RESISTANCE
Thermal resistance values specified in Table 3 are simulated
based on JEDEC specifications, unless specified otherwise, and
must be used in compliance with JESD51-12.
Table 3. Thermal Resistance
Package Type θJA θJC1 θJB ΨJT ΨJB Unit
CP-16-222 39.25 7.5 17.4 0.8 12.4 °C/W
1 For θJC, 100 µm thermal interface material is used. Thermal interface material
is assumed to have 3.6 W/mK.
2 Using enhanced heat removal (printed circuit board (PCB), heat sink, and
airflow) techniques improves thermal resistance values.
ESD CAUTION
Data Sheet ADM8845
Rev. D | Page 5 of 18
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
12
11
10
1
3
49
2
6
5
7
8
16
15
14
13
V
OUT
C2+
I
SET
FB1
C2–
CTRL2
GND
FB6
NOTES
1. CONNECT EXPOSED PADDLE TO GND.
FB2
FB3
FB4
FB5
V
CC
C1+
C1–
CTRL1
04867-0-003
ADM8845
TOP VIEW
(Not to Scale)
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Function
1 VOUT Charge Pump Output. A 2.2 μF capacitor to ground is required on this pin. Connect VOUT to the anodes of all
the LEDs.
2 C2+ Flying Capacitor 2 Positive Connection.
3 ISET Bias Current Set Input. The current, ISET, flowing through the resistor, RSET, is gained up by 120 to give the ILED
current. Connect RSET to GND to set the bias current as VSET/RSET. Note that VSET = 1.18 V.
4 to 9 FB1 to FB6 LED1 to LED6 Cathode Connection and Charge Pump Feedback. The current, ISET, flowing in these LEDs is 120 times
the current flowing through resistor, RSET. When using fewer than six LEDs, this pin can be left unconnected or
connected to GND.
10 GND Device Ground Pin.
11 C2− Flying Capacitor 2 Negative Connection.
12 CTRL2 Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs.
13 CTRL1 Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs.
14 C1− Flying Capacitor 1 Negative Connection.
15 VCC Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7 μF decoupling capacitor.
16 C1+ Flying Capacitor 1 Positive Connection.
EP Exposed Paddle. Connect the exposed paddle to GND.
ADM8845 Data Sheet
Rev. D | Page 6 of 18
TYPICAL PERFORMANCE CHARACTERISTICS
5
10
15
20
25
30
35
10.75
04867-0-004
R
SET
(k)
LED CURRENT (mA)
4.75 6.75 12.75 14.758.75
Figure 3. LED Current vs. RSET
20.00
20.10
20.15
20.20
20.25
20.30
20.35
4.1
04867-0-005
SUPPLY VOLTAGE (V)
LED CURRENT (mA)
2.6 3.1 4.6 5.63.6 5.1
–40C
25C
85C
20.05
Figure 4. LED Current vs. Supply Voltage Over Various Temperatures,
Six LEDs Enabled
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
25
04867-0-006
TEMPERATURE (C)
% ERROR
–40 –20 45 850 65
Figure 5. LED Current Matching over Temperature, VCC = 3.6 V, ILED = 20 mA,
Six LEDs Enabled
–0.4
–0.2
–0.1
0
0.1
0.2
0.4
3.8
04867-0-007
SUPPLY VOLTAGE (V)
MATCHING ERROR (%)
2.6 4.2 5.03.4 4.6
–0.3
0.3
3.0 5.4
MAX NEGATIVE MATCHING ERROR
MAX POSITIVE MATCHING ERROR
Figure 6. ILED Matching Error vs. Supply Voltage,
TA = 25°C and ILED = 20 mA
04867-0-008
TEMPERATURE (C)
LED CURRENT (mA)
–40 0 8040
20.08
20.12
20.14
20.16
20.18
20.20
20.24
20.10
20.22
Figure 7. LED Current Variation over Temperature, VCC = 3.6 V
5
10
15
20
25
30
35
3.8
04867-0-009
SUPPLY VOLTAGE (V)
LED CURRENT (mA)
2.6 3.0 4.6 5.43.4 5.04.2
Figure 8. Lead Current vs. Supply Voltage
WI“ kl’l‘xn iv” ”W
Data Sheet ADM8845
Rev. D | Page 7 of 18
0
4
8
12
16
20
04867-0-010
DUTY CYCLE (%)
LED CURRENT (mA)
0 20 60 1008040
Figure 9. LED Current vs. PWM Dimming (Varying Duty Cycle),
Six LEDs Enabled, Frequency = 1 kHz
0
50
100
150
250
300
04867-0-011
SUPPLY VOLTAGE (V)
SUPPLY CURRENT I
CC
(mA)
2.6 3.0 3.8 4.64.23.4
20mA/LED
15mA/LED
200
5.0 5.4
Figure 10. Supply Current ICC vs. Supply Voltage,
Six LEDs Enabled
04867-0-012
CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV
2
1
BWBW
V
OUT
V
CC
Figure 11. 1.5× Mode Operating Waveforms
60
65
70
80
90
95
04867-0-013
DUTY CYCLE (%)
EFFICIENCY (%)
04060807050
85
90 100
10 20 30
75
Figure 12. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal,
Six LEDs Enabled, 20 mA/LED
04867-0-014
CH2 160mACH1 2.00V M 5.00s CH2 180mV
2
1
BWBW
CURRENT
3
V
OUT
CTRL1/2
CH3 1.00V
Figure 13. Soft Start Showing the Initial In-Rush Current and VOUT Variation,
Six LEDs at 20 mA/LED, VCC = 3.6 V
04867-0-015
CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV
2
1
BWBW
V
OUT
V
CC
Figure 14 .2× Mode Operating Waveform
m:
ADM8845 Data Sheet
Rev. D | Page 8 of 18
04867-0-016
CH2 20.0mVCH1 20.0mV M 400ns CH1 220mV
2
1
BWBW
V
OUT
V
CC
Figure 15. 1× Mode Operating Waveforms
40
45
50
60
80
90
04867-0-017
V
CC
(V)
POWER EFFICIENCY (%)
70
55
65
75
85
V
F
= 4.0V
V
F
= 3.8V
V
F
= 4.3V
V
F
= 3.2V
V
F
= 3.6V
2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1
Figure 16. Power Efficiency vs. VCC over Li-Ion Range,
Six LEDS at 15 mA/LED
40
45
50
60
80
90
04867-0-018
V
CC
(V)
POWER EFFICIEN
C
Y (%)
70
55
65
75
85
V
F
= 4.0V
V
F
= 3.8V
V
F
= 4.3V
V
F
= 3.2V
V
F
= 3.6V
2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1
Figure 17. Power Efficiency vs. VCC over Li-Ion Range,
Four LEDS at 15 mA/LED
40
45
50
60
80
90
04867-0-019
V
CC
(V)
POWER EFFICIEN
C
Y (%)
70
55
65
75
85
V
F
= 4.0V
V
F
= 3.8V
V
F
= 4.3V
V
F
= 3.2V
V
F
= 3.6V
2.8 3.0 3.4 3.83.63.2 4.0 4.22.9 3.1 3.3 3.5 3.7 3.9 4.1
Figure 18. Power Efficiency vs. VCC over Li-Ion Range,
Six LEDS at 20 mA/LED
40
45
50
60
80
90
04867-0-020
V
CC
(V)
POWER EFFICIEN
C
Y (%)
2.8 3.0 3.4 3.83.63.2
70
4.0 4.2
55
65
75
85
2.9 3.1 3.3 3.5 3.7 3.9 4.1
V
F
= 4.0V
V
F
= 3.8V
V
F
= 4.3V
V
F
= 3.2V
V
F
= 3.6V
Figure 19. Power Efficiency vs. VCC over Li-Ion Range
Four LEDS at 20 mA/LED
04867-0-021
CH1 2.00V CH2 2.00V M10.0ms CH2 4.36V
2
1
V
OUT
CTRL1/2 : 44.0ms
@: –44.4ms
C2 FALL
200s
LOW SIGNAL
AMPLITUDE
Figure 20. TPC Delay
Data Sheet ADM8845
Rev. D | Page 9 of 18
04867-0-022
3
0m
A
2
0m
A
65°C 85°C
Figure 21. Maximum ILED vs. Ambient Temperature,
Six LEDs Connected
ADM8845 Data Sheet
Rev. D | Page 10 of 18
THEORY OF OPERATION
The ADM8845 charge pump driver for LCD white LED back-
lights implements a multiple gain charge pump (1×, 1.5×, 2×) to
maintain the correct voltage on the anodes of the LEDs over a
2.6 V to 5.5 V (Li-Ion) input supply voltage. The charge pump
automatically switches between 1×/1.5×/2× modes, based on
the input voltage, to maintain sufficient drive for the LED anodes,
with VCC input voltages as low as 2.6 V. It also includes regula-
tion of the charge pump output voltage for supply voltages up to
5.5 V. The six LEDs of the ADM8845 are arranged into two
groups, main and sub. The main display can have up to four
LEDs, FB1 to FB4, and the sub display can have one or two
LEDs, FB5 and FB6 (see Figure 23). Two digital input control
pins, CTRL1 and CTRL2, control the shutdown operation and
the brightness of the main and sub displays (see Table 5).
Table 5. Shutdown Truth Table
CTRL1 CTRL2 LED Shutdown Operation
0 0 Sub display off/main display off
0 1 Sub display off/main display on
1 0 Sub display on/main display off
1 1 Sub display on/main display on
An external resistor, RSET, is connected between the ISET pin and
GND. This resistor sets up a reference current, ISET, which is
internally gained up by 120 within the ADM8845 to produce
the ILED currents of up to 30 mA/LED (ILED = ISET × 120 and
ISET = 1.18 V/RSET). The ADM8845 uses six individual current
sinks to individually sense each LED current with a maximum
matching performance of 1%. This current matching perform-
ance ensures uniform brightness across a color display.
The ADM8845 lets the user control the brightness of the white
LEDs with a digital PWM signal applied to CTRL1 and/or
CTRL2. The duty cycle of the applied PWM signal determines
the brightness of the main and/or sub display backlight white
LEDs. The ADM8845 also allows the brightness of the white
LEDs to be controlled using a dc voltage (see Figure 22). Soft-
start circuitry limits the in-rush current flow at power-up. The
ADM8845 is fabricated using CMOS technology for minimal
power consumption and is packaged in a 16-lead lead frame
chip scale package.
ISET
RSET = 13.4k
R = 15k
VBRIGHT
0V–2.5V
ADM8845
04867-0-027
Figure 22. PWM Brightness Control Using a DC Voltage Applied to VBRIGHT
CURRENT
CONTROL 1
CURRENT
CONTROL 2
CURRENT
CONTROL 3
CURRENT
CONTROL 4
CURRENT
CONTROL 5
CURRENT
CONTROL 6
CONTROL
LOGIC V
REF
CHARGE PUMP
1/1.5/2 MODE
OSC
LED
CURRENT
CONTROL
CIRCUIT
FB1
CURRENT CONTROLLED SINKS
FB2
FB3
FB4
FB5
FB6
V
OUT
C4
4.7F
V
CC
C1
1F
CTRL1
CTRL2
C2
1F
R
SET
I
SET
GND
C3
2.2F
ADM8845
04867-0-001
MAIN SUB
Figure 23. Functional Block Diagram
Data Sheet ADM8845
Rev. D | Page 11 of 18
OUTPUT CURRENT CAPABILITY
The ADM8845 can drive up to 30 mA of current to each of the
six LEDs given an input voltage of 2.6 V to 5.5 V. The LED
currents have a maximum current matching of 1% between any
two LED currents. An external resistor, RSET, sets the output
current, approximated by the following equation:
RSET = 120 × (1.18 V/ILED)
To regulate the LED currents properly, sufficient headroom
voltage (compliance) must be present. The compliance refers to
the minimum amount of voltage that must be present across the
internal current sinks to ensure that the desired current and
matching performance can be realized. To ensure that the
desired current is obtained, use the following equation to find
the minimum input voltage required:
VOUT − VF ≥ Compliance
where VF is the LED forward voltage. For 20 mA/LED, the
compliance is 0.20 V typical and 0.30 V maximum (see Table 6).
Table 6. ILED, RSET, and Compliance Table
ILED (mA) RSET (kΩ) Typical Compliance (V)
15 9.44 0.17
20 7.08 0.20
30 4.72 0.34
When the ADM8845 charge pump is loaded with 180 mA
(six LEDs at 30 mA/LED), the ambient operating temperature
is reduced (see Figure 21).
AUTOMATIC GAIN CONTROL
The automatic gain control block controls the operation of the
charge pump by selecting the appropriate gain for the charge
pump. This maintains sufficient drive for the LED anodes at
the highest power efficiency over a 2.6 V to 5.5 V input supply
range. The charge pump switching thresholds are described in
Table 7.
Table 7. Charge Pump Switching Thresholds
Gain Threshold (V)
1.5× to 2× 3.33
2× to 1.5× 3.36
1× to 1.5× 4.77
1.5× to 1× 4.81
CURRENT MATCHING
The 1% maximum current matching performance is defined by
the following equations:
IAVG = (IMAX + IMIN)/2
Maximum Matching Error = [(IMAX − IAVG)/IAVG] × 100
or
Minimum Matching Error = [(IMIN − IAVG)/IAVG] × 100
where:
IMAX is the largest ILED current.
IMIN is the smallest ILED current.
BRIGHTNESS CONTROL WITH A DIGITAL PWM
SIGNAL
PWM brightness control provides the widest brightness control
method by pulsing the white LEDs on and off using the digital
input control pins, CTRL1 and/or CTRL2. PWM brightness
control also removes any chromaticity shifts associated with
changing the white LED current, because the LEDs operate
either at zero current or full current (set by RSET).
The digital PWM signal applied with a frequency of 100 Hz to
200 kHz turns the current control sinks on and off using CTRL1
and/or CTRL2. The average current through the LEDs changes
with the PWM signal duty cycle. If the PWM frequency is much
less than 100 Hz, flicker could be seen in the LEDs. For the
ADM8845, zero duty cycle turns off the LEDs, and a 50% duty
cycle results in an average LED current ILED being half the pro-
grammed LED current. For example, if RSET is set to program
20 mA/LED, a 50% duty cycle results in an average ILED of
10 mA/LED, ILED being half the programmed LED current.
FB1
FB2
FB3
FB4
FB5
FB6
V
OUT
C1
1F
CTRL1
CTRL2
C2
1F
R
SET
I
SET
C3
2.2F
ADM8845
PWM INPUT
OR HIGH/LOW
PWM INPUT
OR HIGH/LOW
04867-0-024
Figure 24. Digital PWM Brightness Control Application Diagram
By applying a digital PWM signal to the digital input control
pins, CTRL1 and/or CTRL2 can adjust the brightness of the sub
and/or main displays. The six white LEDs of the ADM8845 are
organized into two groups: main display, FB1 to FB4, and sub
display, FB5 and FB6. For more information, refer to the Theory
of Operation section.
ADM8845 Data Sheet
Rev. D | Page 12 of 18
The main and sub display brightness of the ADM8845 can be
controlled together or separately by applying a digital PWM
signal to both CTRL1 and CTRL2 pins. The duty cycle of the
applied digital PWM signal determines the brightness of the
main and sub displays together. Varying the duty cycle of the
applied PWM signal also varies the brightness of the main and
sub displays from 0% to 100%.
By holding CTRL1 low and applying a digital PWM signal to
CTRL2, the sub display is turned off and the main display is
turned on. The brightness of the main display is then determined
by the duty cycle of the applied digital PWM signal.
By applying a digital PWM signal to CTRL1 and holding CTRL2
low, the sub display is turned on and the main display is turned
off. Then the brightness of the sub display is determined by the
duty cycle of the applied digital PWM signal.
By applying a digital PWM signal to CTRL1 and holding CTRL2
high, the sub display is turned on and the main display is turned
on. Then the brightness of the sub display is determined by the
duty cycle of the applied digital PWM signal. The brightness of
the main display is set to the maximum, which is set by RSET.
By holding CTRL1 high and applying a digital PWM signal to
CTRL2, the sub display is turned on and the main display is
turned on. Then the brightness of the main display is determined
by the duty cycle of the applied digital PWM signal. The bright-
ness of the sub display is set to the maximum, which is set by RSET.
When CTRL1 and CTRL2 go low, the LED current control
sinks shutdown. Shutdown of the charge pump is delayed by
15 ms. This timeout period (tCP) allows the ADM8845 to
determine if a digital PWM signal is present on CTRL1 and
CTRL2 or if the user has selected a full chip shutdown (see
Figure 25).
If digital PWM brightness control of the LEDs is not required, a
constant logic level 1 (VCC) or 0 (GND) must be applied.
The six white LEDs in the ADM8845 are arranged in two groups,
sub and main. It is possible to configure the six LEDs as in
Table 8. For more information, also refer to Figure 25.
Table 8. Digital Inputs Truth Table
CTRL1 CTRL2 LED Operation
0 0 Sub display off/main display off (full shutdown) 1, 2
0 1 Sub display off/main display on1, 3
1 0 Sub display on/main display off 4, 2
1 1 Sub display on/main display on (full on)4, 3
0 PWM Sub display off/digital PWM brightness control on main display1, 5
PWM 0 Digital PWM brightness control on sub display/main display off5, 2
1 PWM Sub display on/ digital PWM brightness control on main display4, 5
PWM 1 Digital PWM brightness control on sub display/main display on5
PWM PWM Digital PWM brightness control on sub and main display5
1 Sub display off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1.
2 Main display off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2.
3 Main display on means the display is on with the maximum brightness set by the RSET resistor. CTRL2 = 1 means a constant logic level (VCC) is applied to CTRL2.
4 Sub display on means the display is on with the maximum brightness set by the RSET resistor. CTRL1 = 1 means a constant logic level (VCC) is applied to CTRL1.
5 PWM means a digital PWM signal is applied to the CTRL1 and/or the CTRL2 pin with a frequency from 100 Hz to 200 kHz.
L L L L _|_L_l_|_l_ _l_L_l_ _|_L_l_ _l_L_l_
Data Sheet ADM8845
Rev. D | Page 13 of 18
LED CONFIG.
FULL ON MAIN AND SUB OFF
CTRL1
CTRL2
V
OUT
I
LED
(SUB)
I
LED
(MAIN)
SUB DISPLAY
BRIGHTNESS
MAIN DISPLAY
BRIGHTNESS
37ms >
t
CP
> 15ms
SHDN
SHDN
50%
50%
100%
100%
80%
t
CP
04867-0-025
SUB AND MAIN 50%
DUTY CYCLE
MAIN 80% DUTY CYCLE,
SUB OFF
Figure 25. Application Timing
LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO VPWM
Adding two external resistors and a capacitor, as shown in
Figure 26, can also be used to control PWM brightness. This
PWM brightness control method can be used instead of CTRL1
and/or CTRL2 digital PWM brightness control. With this con-
figuration, the CTRL1 and CTRL2 digital logic pins can be used
to control shutdown of the white LEDs, while VPWM can be used
to control the brightness of all the white LEDs by applying a
high frequency PWM signal (amplitude 0 V to 2.5 V) to drive
an R-C-R filter on the ISET pin of the ADM8845. A 0% PWM
duty cycle corresponds to 20 mA/LED, while a 100% PWM
duty cycle corresponds to a 0 mA/LED. At PWM frequencies
above 5 kHz, C5 may be reduced (see Figure 26). To have 20 mA
flowing in each LED, the amplitude of the PWM signal must be
0 V and 2.5 V only.
100
)1(
120
2
2
_CycleDuty
RR
RR
VoltageI
I
SET
SET
SET
LED
I
SET
R
SET
= 13.4k
R = 7.5k
V
PWM
0V–2.5V
ADM8845
04867-0-026
100% = I
LED
= 0mA
0% = I
LED
= 20mA
R = 7.5k
C5 = 1F
Figure 26. PWM Brightness Control Using Filtered PWM Signal
LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO VBRIGHT
By adding one resistor, as in Figure 22, this configuration can
control the brightness of the white LEDs using a dc voltage
applied to the VBRIGHT node. Figure 27 shows an application
example of LED brightness control using a dc voltage with a
amplitude of 0 V to 2.5 V, applied to VBRIGHT.
The equation for ILED is
ISET = [(1/RSET + 1/R)(VSET)] − [(1/R)(VBRIGHT)]
ILED = 120 × ISET
where:
R = 15 kΩ.
VSET the voltage at ISET pin (1.18 V).
V
BRIGHT
04867-0-028
I
LED
2.5V
0mA
1.6V
7.2mA
0.8V
13.6mA
0V
20mA
Figure 27. PWM Brightness Control Application Diagram Using a
DC Voltage Applied to VBRIGHT
ADM8845 Data Sheet
Rev. D | Page 14 of 18
APPLICATIONS INFORMATION
LAYOUT CONSIDERATIONS AND NOISE
Because of the s switching behavior of the ADM8845, PCB
trace layout is an important consideration. To ensure optimum
performance, a ground plane should be used, and all capacitors
(C1, C2, C3, C4) must be located with minimal track lengths to
the pins of the ADM8845.
WHITE LED SHORTING
If an LED is shorted, the ADM8845 continues to drive the
remaining LEDs with ILED per LED (ILED = ISET × 120 mA). This
is because the ADM8845 uses six internal currents sinks to
produce the LED current. If an LED is shorted, the ADM8845
continues to sink (ISET × 120 mA) as programmed by RSET
through the shorted LED.
DRIVING FEWER THAN SIX LEDs
The ADM8845 can be operated with fewer than six LEDs in
parallel by simply leaving the unused FBx pins floating or
connected to GND. For example, Figure 28 shows five LEDs
being powered by the ADM8845, and Figure 29 shows three
main LEDs and one sub LED.
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
04867-0-029
LCD
Figure 28. Driving Five White LEDs
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
R
SET
I
SET
04867-0-030
MAIN DISPLAY
SUB DISPLAY
Figure 29. Driving Three Main LEDs and One Sub LED
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
R
SET
I
SET
04867-0-002
MAIN DISPLAY
SUB DISPLAY
Figure 30. Typical Application Diagram
Data Sheet ADM8845
Rev. D | Page 15 of 18
DRIVING FLASH LEDS
The ADM8845 can be operated with any two FBx pins used in
parallel to double the combined LED current supplied by the
ADM8845. For example, if three flash LEDs need to be driven
with 60 mA/LED, the ADM8845 can be configured as in
Figure 31 (see also Figure 21).
V
OUT
FB1
FB2
FB3
FB4
FB5
FB6
V
CC
2.6V–5.5V
CTRL1
CTRL2
GND
ADM8845
R
SET
.27
04867-0-031
60mA 60mA 60mA
Figure 31. Driving Three Flash LEDs
DRIVING CAMERA LIGHT, MAIN, AND SUB LEDs
The ADM8845 can be configured to power a camera light that
is composed of four white LEDs in parallel, along with the main
and sub display bundled into one package. FB1 to FB4 now
power the camera light, and FB5 and FB6 power the main
display. The sub display LED is powered from the ADM8845 by
using an external current mirror to control the current flowing
through the sub white LED (see Figure 32). All white LEDs have
15 mA/LED. Total load on the ADM8845 charge pump is
therefore 105 mA, and the maximum load on the ADM8845
charge pump is 180 mA (see Figure 21).
CURRENT
CONTROL 1
CURRENT
CONTROL 2
CURRENT
CONTROL 3
CURRENT
CONTROL 4
CURRENT
CONTROL 5
CURRENT
CONTROL 6
CONTROL
LOGIC V
REF
CHARGE PUMP
1/1.5/2 MODE
OSC
LED
CURRENT
CONTROL
CIRCUIT
FB1
CURRENT CONTROLLED SINKS
FB2
FB3
FB4
FB5
FB6
V
OUT
C4
4.7F
VCC
C1
1F
CTRL1
CTRL2
C2
1F
R
SET
9.44k
I
SET
GND
C3
2.2F
ADM8845
04867-0-032
15mA/LED 15mA/LED 15mA/LED
CURRENT
CONTROL7
R
CAMERA MAIN SUB
Figure 32. Driving Camera Light, Two Main LEDs, and One Sub LED
WH
ADM8845 Data Sheet
Rev. D | Page 16 of 18
DRIVING FOUR BACKLIGHT WHITE LEDS AND
FLASH LEDS
The ADM8845 can be configured to power four backlight white
LEDs and a camera flash, bundled into one package. FB1 to FB4
power the backlight light, FB5 and FB6 power two of the flash
LEDs, while the third is powered by an external current mirror
to control the current flowing through the third flash LED (see
Figure 33). All the backlight white LEDs have 15 mA/LED, and
the flash current is 20 mA/LED. The total load on the
ADM8845 charge pump is 120 mA; the maximum load on
the ADM8845 charge pump is 180 mA (see Figure 21).
CTRL1 controls the flash on/off, and CTRL2 controls the back-
light on/off and brightness control. Because the RSET resistor sets
the current that each of the six current control blocks can sink,
a PWM signal is used to change the current in the backlight
from 20 mA to 5 mA/LED. The CTRL2 duty cycle is 15/20 to
give 15 mA/backlight LED.
04867-0-034
CURRENT
CONTROL 1
CURRENT
CONTROL 2
CURRENT
CONTROL 3
CURRENT
CONTROL 4
CURRENT
CONTROL 5
CURRENT
CONTROL 6
CONTROL
LOGIC
V
REF
CHARGE PUMP
1×/1.5×/2× MODE
OSC
LED
CURRENT
CONTROL
CIRCUIT
FB1
CURRENT CONTROLLED SINKS
FB2
FB3
FB4
FB5
FB6
V
OUT
C4
4.7F
V
CC
CTRL1
CTRL2
C2
1F
C1
1F
R
SET
7.32k
I
SET
GND
C3
2.2F
ADM8845
15mA/LED 20mA/LED
CURRENT
CONTROL 7
R
BACK-
LIGHT FLASH
Figure 33. Driving Four Backlight LEDs and Flash LED
Data Sheet ADM8845
Rev. D | Page 17 of 18
POWER EFFICIENCY
The ADM8845 power efficiency (η) equations are the following:
η = POUT/PIN
PIN = ((VCC × ILOAD × Gain) + (IQ × VCC))
POUT = 6 × (VF × ILED)
where:
Gain is equal to the charge pump mode (1×, 1.5×, 2×).
IQ is the quiescent current of the ADM8845, 2.6 mA.
VF is the LED forward voltage.
FB1
FB2
FB3
FB4
FB5
FB6
V
OUT
CTRL1
CTRL2
R
SET
I
SET
ADM8845
04867-0-033
V
CC
3.4V
V
CC
GND
I
LOAD
I
IN
Figure 34. Charge Pump Power Efficiency Diagram
Example 1 and Example 2 show calculations of the ADM8845
power efficiency. See Figure 34 as well.
Example 1
The ADM8845 driving six white LEDs with a 20 mA/LED at
VCC = 3.4 V (1.5× mode) and LED VF = 4.5 V.
PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))
PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
PIN = ((0.612) + (0.00884))
PIN = 0.62084
POUT = 6 × (VF × ILED)
POUT = 6 × (4.5 V × 20 mA)
POUT = 0.54
η = POUT/PIN
η = 0.54/0.62084
η = 87%
Example 2
The ADM8845 driving six white LEDs with a 20 mA/LED at
VCC = 3.4 (1.5× mode) and LED VF = 3.6 V.
PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))
PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
PIN = ((0.612) + (0.00884))
PIN = 0.62084
POUT = 6 × (VF × ILED)
POUT = 6 × (3.6 V × 20 mA)
POUT = 0.432
η = POUT/PIN
η = 0.432/0.62084
η = 70%
fi k: a @‘r '1 T W \ w 1 ,iL, 7 : ¥ : EL; , f T‘ SEQEOECS; www.ana|ng.cum
ADM8845 Data Sheet
Rev. D | Page 18 of 18
OUTLINE DIMENSIONS
0.30
0.23
0.18
1.75
1.60 SQ
1.45
3.10
3.00 SQ
2.90
1
0.50
BSC
BOTTOM VIEWTOP VIEW
16
5
8
9
12
13
4
0.50
0.40
0.30
0.05 MAX
0.02 NOM
0.20 REF
0.20 MIN
COPLANARITY
0.08
PIN 1
INDICATOR
0.80
0.75
0.70
COMPLIANT
TO
JEDEC STANDARDS MO-220-WEED-6.
PKG-005138
SEATING
PLANE
SIDE VIEW
EXPOSED
PAD
02-23-2017-E
PIN 1
INDIC
A
TOR AREA OPTIONS
(SEE DETAIL A)
DETAIL A
(JEDEC 95)
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
Figure 35. 16-Lead Lead Frame Chip Scale Package [LFCSP]
3 mm × 3 mm Body and 0.75 mm Package Height
(CP-16-22)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option Marking Code
ADM8845ACPZ-REEL7 −40°C to + 85°C 16-Lead Lead Frame Chip Scale Package [LFCSP] CP-16-22 M5G
ADM8845EB-EVALZ Evaluation Board
1 Z = RoHS Compliant Part.
©2004–2018 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04867-0-5/18(D)