LTC3638 Datasheet by Analog Devices Inc.

View All Related Products | Download PDF Datasheet
LTLII‘IM TECHNOLOGY (MW) ssm BMW 1—; EFFICIENCY ( /) a. I L [Li , POWER L05 L7 LJUW 1
LTC3638
1
3638fa
For more information www.linear.com/LTC3638
TYPICAL APPLICATION
FEATURES DESCRIPTION
High Efficiency, 140V
250mA Step-Down
Regulator
The LTC
®
3638 is a high efficiency step-down DC/DC
regulator with internal power switch that draws only 12μA
typical DC supply current while maintaining a regulated
output voltage at no load.
The LTC3638 can supply up to 250mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency and for reduc-
ing output ripple and component size. The LTC3638’s
combination of Burst Mode
®
operation, integrated power
switch, low quiescent current, and programmable peak
current limit provides high efficiency over a broad range
of load currents.
With its wide input range of 4V to 140V and programmable
overvoltage lockout, the LTC3638 is a robust regulator
suited for regulating from a wide variety of power sources.
Additionally, the LTC3638 includes a precise run threshold
and soft-start feature to guarantee that the power system
start-up is well-controlled in any environment. A feedback
comparator output enables multiple LTC3638s to be con-
nected in parallel for higher current applications.
The LTC3638 is available in a thermally enhanced high
voltage-capable 16-lead MSE package with four missing pins.
L, LT, LT C, LT M, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Efficiency and Power Loss vs Load Current
5V to 140V Input to 5V Output, 250mA Step-Down Regulator
APPLICATIONS
n Wide Operating Input Voltage Range: 4V to 140V
n Internal Low Resistance Power MOSFET
n No Compensation Required
n Adjustable 20mA to 250mA Maximum Output
Current
n Low Dropout Operation: 100% Duty Cycle
n Low Quiescent Current: 12µA
n Wide Output Range: 0.8V to VIN
n 0.8V ±1% Feedback Voltage Reference
n Precise RUN Pin Threshold
n Internal or External Soft-Start
n Programmable 1.8V, 3.3V, 5V or Adjustable Output
n Few External Components Required
n Programmable Input Overvoltage Lockout
n Thermally Enhanced High Voltage MSOP Package
n Industrial Control Supplies
n Medical Devices
n Distributed Power Systems
n Portable Instruments
n Battery-Operated Devices
n Avionics
n Automotive
3638 TA01a
VFB
SS
SW
L1
220µH
VIN
RUN
CIN
F
250V COUT
22µF
VIN
5V TO 140V
VOUT
5V
250mA
OVLO
LTC3638
GND
VPRG2 VPRG1
VIN = 12V
VIN = 48V
VIN = 140V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
90
100
20
10
80
50
70
10
1
100
1000
60
40
0.1 100 1000
3638 TA01b
0101
EFFICIENCY
POWER LOSS
LTC3638 TOPWEW E r 1 3 W4 a r I: \ \ :I \ \ I: \ ‘ :l I: ‘ ‘ j E rpm: 3 E k u j MSE PACKAGE VARWIDN Mszm) ‘arLEAD PLAS‘HC MSOP
LTC3638
2
3638fa
For more information www.linear.com/LTC3638
ABSOLUTE MAXIMUM RATINGS
1
3
5
6
7
8
SW
VIN
FBO
V
PRG2
V
PRG1
GND
16
14
12
11
10
9
GND
RUN
OVLO
ISET
SS
VFB
TOP VIEW
17
GND
MSE PACKAGE
VARIATION: MSE16 (12)
16-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 40°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
PIN CONFIGURATION
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3638EMSE#PBF LTC3638EMSE#TRPBF 3638 16-Lead Plastic MSOP –40°C to 125°C
LTC3638IMSE#PBF LTC3638IMSE#TRPBF 3638 16-Lead Plastic MSOP –40°C to 125°C
LTC3638HMSE#PBF LTC3638HMSE#TRPBF 3638 16-Lead Plastic MSOP –40°C to 150°C
LTC3638MPMSE#PBF LTC3638MPMSE#TRPBF 3638 16-Lead Plastic MSOP –55°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping
container.Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
VIN Supply Voltage ................................... 0.3V to 140V
RUN Voltage............................................. 0.3V to 140V
SS, FBO, OVLO, ISET Voltages ...................... 0.3V to 6V
VFB, VPRG1, VPRG2 Voltages ......................... 0.3V to 6V
Operating Junction Temperature Range (Notes 2, 3, 4)
LTC3638E, LTC3638I ......................... 40°C to 125°C
LTC3638H ..........................................40°C to 150°C
LTC3638MP ....................................... 5C to 150°C
Storage Temperature Range ..................6C to 150°C
Lead Temperature (Soldering, 10 sec) ...................300°C
(Note 1)
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Supply (VIN)
VIN Input Voltage Operating Range 4 140 V
VOUT Output Voltage Operating Range 0.8 VIN V
UVLO VIN Undervoltage Lockout VIN Rising
VIN Falling
Hysteresis
l
l
3.5
3.3 3.75
3.5
250
4.0
3.8 V
V
mV
IQDC Supply Current (Note 5)
Active Mode
Sleep Mode
Shutdown Mode
No Load
VRUN = 0V
150
12
1.4
350
22
6
µA
µA
µA
VRUN RUN Pin Threshold RUN Rising
RUN Falling
Hysteresis
1.17
1.06 1.21
1.10
110
1.25
1.14 V
V
mV
IRUN RUN Pin Leakage Current RUN = 1.3V –10 0 10 nA
VOVLO OVLO Pin Threshold OVLO Rising
OVLO Falling
Hysteresis
1.17
1.06 1.21
1.10
110
1.25
1.14 V
V
mV
LTC3638
LTC3638
3
3638fa
For more information www.linear.com/LTC3638
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Supply (VFB)
VFB(ADJ) Feedback Comparator Threshold
(Adjustable Output) VFB Rising, VPRG1 = VPRG2 = 0V
LTC3638E, LTC3638I
LTC3638H, LTC3638MP
l
l
0.792
0.788
0.800
0.800
0.808
0.812
V
V
VFBH Feedback Comparator Hysteresis
(Adjustable Output) VFB Falling, VPRG1 = VPRG2 = 0V l3 5 9 mV
IFB Feedback Pin Current VFB = 1V, VPRG1 = VPRG2 = 0V –10 0 10 nA
VFB(FIXED) Feedback Comparator Thresholds
(Fixed Output) VFB Rising, VPRG1 = SS, VPRG2 = 0V
VFB Falling, VPRG1 = SS, VPRG2 = 0V
l
l
4.94
4.91 5.015
4.985 5.09
5.06 V
V
VFB Rising, VPRG1 = 0V, VPRG2 = SS
VFB Falling, VPRG1 = 0V, VPRG2 = SS
l
l
3.25
3.23 3.31
3.29 3.37
3.35 V
V
VFB Rising, VPRG1 = VPRG2 = SS
VFB Falling, VPRG1 = VPRG2 = SS
l
l
1.78
1.77 1.81
1.80 1.84
1.83 V
V
Operation
IPEAK Peak Current Comparator Threshold ISET Floating
100k Resistor from ISET to GND
ISET Shorted to GND
l
l
l
500
250
40
575
300
60
650
350
80
mA
mA
mA
RON Power Switch On-Resistance ISW = –100mA 1.8 Ω
ILSW Switch Pin Leakage Current VIN = 140V, SW = 0V 0.1 1 μA
ISS Soft-Start Pin Pull-Up Current VSS < 2.5V 4 5 6 μA
tINT(SS) Internal Soft-Start Time SS Pin Floating 1 ms
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: The LTC3638 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3638E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3638I is guaranteed
over the –40°C to 125°C operating junction temperature range, the
LTC3638H is guaranteed over the –40°C to 150°C operating junction
temperature range and the LTC3638MP is tested and guaranteed over the
–55°C to 150°C operating junction temperature range.
High junction temperatures degrade operating lifetimes; operating lifetime
is derated for junction temperatures greater than 125°C. Note that the
maximum ambient temperature consistent with these specifications is
determined by specific operating conditions in conjunction with board
layout, the rated package thermal impedance and other environmental
factors.
Note 3: The junction temperature (TJ, in °C) is calculated from the ambient
temperature (TA, in °C) and power dissipation (PD, in Watts) according to
the formula:
TJ = TA + (PDθJA)
where θJA is 40°C/W for the MSOP package.
Note that the maximum ambient temperature consistent with these
specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors.
Note 4: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device. The overtemperature protection level is not production tested.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
LTC3638 mu mu wn :3 EEEEW 552$ :2 55.2% S #2:? 32$me 35 5 22¢ x /\ 302 mu :3; MESS 32$me :3 55.2% 700 mu 2E Emmi; x51 25:51.50 x51 / sun :E V 32%;: AECEES xml L7HCU§QB
LTC3638
4
3638fa
For more information www.linear.com/LTC3638
TYPICAL PERFORMANCE CHARACTERISTICS
Peak Current Trip Threshold
vs RISET
Efficiency vs Load Current,
VOUT = 5V
Peak Current Trip Threshold
vs Temperature and ISET
Efficiency vs Load Current,
VOUT = 3.3V
Peak Current Trip Threshold
vs Input Voltage
Efficiency vs Load Current,
VOUT = 1.8V
Efficiency vs Input Voltage,
VOUT = 5V
Feedback Comparator Trip
Threshold vs Temperature
RUN and OVLO Thresholds vs
Temperature
0.1 100
1000
101
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
3638 G01
0
FIGURE 14 CIRCUIT
VIN = 12V
VIN = 48V
VIN = 140V
30
90
100
20
10
80
50
70
60
40
00 25 75 100
50 125
150
INPUT VOLTAGE (V)
EFFICIENCY (%)
3638 G04
ILOAD = 250mA
ILOAD = 10mA
ILOAD = 1mA
FIGURE 14 CIRCUIT
TEMPERATURE (°C)
–55
798
799
800
801
–25 5 35 65
95 125
RISET (kΩ)
0
200
300
400
500
600
175
3638 G07
100
50 1007525 125 150
200
0
PEAK CURRENT TRIP THRESHOLD (mA)
TEMPERATURE (°C)
–55
PEAK CURRENT (mA)
100
200
155
3638 G08
05 65–25 35 95 125
700
600
300
400
500
ISET OPEN
ISET = GND
RISET = 100kΩ
100
200
0
700
600
300
400
500
VIN VOLTAGE (V)
0
PEAK CURRENT (mA)
150
3638 G09
60
30 90 120
ISET OPEN
ISET = GND
RISET = 100kΩ
TEMPERATURE (°C)
–55
RUN OR OVLO THRESHOLD VOLTAGE (V)
1.20
1.22
1.24
35 95
3638 G06
1.18
1.16
1.14
1.12
1.10
–25 5 65 125
155
1.08
1.06
RISING
FALLING
0.1 100
1000
101
FIGURE 14 CIRCUIT
VIN = 12V
VIN = 48V
VIN = 140V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
3638 G02
00.1 100
1000
101
FIGURE 14 CIRCUIT
VIN = 12V
VIN = 48V
VIN = 140V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
3638 G03
0
LTC3638 15 ‘5 1 i I <3 i="" f="" e="" e="" e="" §="" :2="" k="" 5="" e="" 5="" z="" 3="" e="" \‘="" 5="" §="" §=""> > 5 ‘ ‘ umowu 5 a u a _H‘ i,‘u’/v\‘l}‘x"( HIE $ % S \ s // v =Aav I x / vw = 3 av E E 1mm ZSDmA LDA E g Heuansmncun uuwm 0mm ,44LLJL; ‘ . w I / u\‘\‘\i\‘\\4\ \\\I\‘\\ W W FIGURE 15 wow L7 HEW 5
LTC3638
5
3638fa
For more information www.linear.com/LTC3638
TYPICAL PERFORMANCE CHARACTERISTICS
Switch On-Resistance
vs Input Voltage
Switch On-Resistance
vs Temperature Load Step Transient Response
Quiescent Supply Current
vs Input Voltage
Operating Waveforms, VIN = 48V
Quiescent Supply Current
vs Temperature
Operating Waveforms, VIN = 140V
Switch Pin Current
vs Temperature
Short-Circuit and Recovery
VIN VOLTAGE (V)
0
0
V
IN
SUPPLY CURRENT (µA)
15
60 90
3638 G10
10
5
30 120
150
SLEEP
SHUTDOWN
VIN VOLTAGE (V)
1.0
SWITCH ON-RESISTANCE (Ω)
2.0
1.5
2.5
3.0
3638 G13
060 90
30 120
150
TEMPERATURE (°C)
–55
SWITCH ON-RESISTANCE (Ω)
35
3638 G14
2
–25 5 65
0
1
4
3
95 125
155
ISW = 250mA
TEMPERATURE (°C)
55 –25
0
V
IN
SUPPLY CURRENT (µA)
10
35
30
25
565 95
3638 G11
5
20
15
35 125
155
VIN = 140V
SLEEP
SHUTDOWN
TEMPERATURE (°C)
–55
SWITCH PIN CURRENT (µA)
35
3638 G12
–5
–25 5 65
–15
15
10
5
0
–10
95 125
155
VIN = 140V
SLEEP MODE
SW = 0.8V
CURRENT INTO SW
SW = 0V
CURRENT OUT OF SW
OUTPUT
VOLTAGE
50mV/DIV
LOAD
CURRENT
100mA/DIV
200µs/DIVVIN = 48V
VOUT = 3.3V
1mA TO 250mA LOAD STEP
FIGURE 15 CIRCUIT
3638
G15
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
20V/DIV
INDUCTOR
CURRENT
500mA/DIV
10µs/DIVVIN = 48V
VOUT = 3.3V
IOUT = 250mA
FIGURE 15 CIRCUIT
3638
G16
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
50V/DIV
INDUCTOR
CURRENT
500mA/DIV
10µs/DIVVIN = 140V
VOUT = 3.3V
IOUT = 250mA
FIGURE 15 CIRCUIT
3638
G17
OUTPUT
VOLTAGE
1V/DIV
INDUCTOR
CURRENT
500mA/DIV
500µs/DIV
FIGURE 15 CIRCUIT
3638
G18
LTC3638 6 L7LJ1‘JW
LTC3638
6
3638fa
For more information www.linear.com/LTC3638
PIN FUNCTIONS
SW (Pin 1): Switch Node Connection to Inductor and
Catch Diode Cathode. This pin connects to the drain of
the internal power MOSFET switch.
VIN (Pin 3): Main Supply Pin. A ceramic bypass capacitor
should be tied between this pin and GND.
FBO (Pin 5): Feedback Comparator Output. Connect to the
VFB pins of additional LTC3638s to combine the output
current. The typical pull-up current is 20µA. The typical pull-
down impedance is 70Ω. See Applications Information.
VPRG2, VPRG1 (Pins 6, 7): Output Voltage Selection. Short
both pins to ground for a resistive divider programmable
output voltage. Short VPRG1 to SS and short VPRG2 to
ground for a 5V output voltage. Short VPRG1 to ground
and short VPRG2 to SS for a 3.3V output voltage. Short
both pins to SS for a 1.8V output voltage.
GND (Pin 8, 16, Exposed Pad Pin 17): Ground. The ex-
posed pad must be soldered to the PCB ground plane for
rated thermal performance.
VFB (Pin 9): Output Voltage Feedback. When configured
for an adjustable output voltage, connect to an external
resistive divider to divide the output voltage down for
comparison to the 0.8V reference. For the fixed output
configuration, directly connect this pin to the output.
SS (Pin 10): Soft-Start Control Input. A capacitor to
ground at this pin sets the output voltage ramp time. A
50µA current initially charges the soft-start capacitor until
switching begins, at which time the current is reduced to
its nominal value ofA. The output voltage ramp time
from zero to its regulated value is 1ms for every 6.25nF
of capacitance from SS to GND. If left floating, the ramp
time defaults to an internal 1ms soft-start.
ISET (Pin 11): Peak Current Set Input. A resistor from this
pin to ground sets the peak current comparator threshold.
Leave floating for the maximum peak current (575mA
typical) or short to ground for minimum peak current
(60mA typical). The maximum output current is one-half
the peak current. TheA current that is sourced out of
this pin when switching is reduced toA in sleep. Op-
tionally, a capacitor can be placed from this pin to GND
to trade off efficiency for light load output voltage ripple.
See Applications Information.
OVLO (Pin 12): Overvoltage Lockout Input. Connect to
the input supply through a resistor divider to set the over-
voltage lockout level. A voltage on this pin above 1.21V
disables the internal MOSFET switch. Normal operation
resumes when the voltage on this pin decreases below
1.10V. Exceeding the OVLO lockout threshold triggers a
soft-start reset, resulting in a graceful recovery from an
input supply transient. Tie this pin to ground if the over-
voltage is not used.
RUN (Pin 14): Run Control Input. A voltage on this pin
above 1.21V enables normal operation. Forcing this pin
below 0.7V shuts down the LTC3638, reducing quiescent
current to approximately 1.4µA. Optionally, connect to the
input supply through a resistor divider to set the under-
voltage lockout.
LTC3638 L7 LJUW
LTC3638
7
3638fa
For more information www.linear.com/LTC3638
BLOCK DIAGRAM
COUT
CIN
VIN
V
OUT
+
+
+
+
3
D1
+
+
+
PEAK CURRENT
COMPARATOR
SWITCH NODE
COMPARATOR
FEEDBACK
COMPARATOR VOLTAGE
REFERENCE
VPRG2
GND
GND
SS
SS
VPRG1
GND
SS
GND
SS
R1
1.0M
4.2M
2.5M
1.0M
R2
800k
800k
800k
VOUT
ADJUSTABLE
5V FIXED
3.3V FIXED
1.8V FIXED
START-UP: 50µA
NORMAL: 5µA
IMPLEMENT DIVIDER
EXTERNALLY FOR
ADJUSTABLE VERSION
VIN
1
SW L1
GND
LOGIC
16
SS
R2
R1
5V
5V
20µA
FBO
70Ω 10
5
GND
8
GND
17
VFB 9
VPRG1 7
VPRG2
3638 BD
6
0.800V
OVLO
1.21V
12
1.21V
RUN
14
ISET
11
ACTIVE: 5µA
SLEEP: 1µA
1.3V
LTC3638
LTC3638
8
3638fa
For more information www.linear.com/LTC3638
OPERATION
The LTC3638 is a step-down DC/DC regulator with internal
power switch that uses Burst Mode control, combining
low quiescent current with high switching frequency,
which results in high efficiency across a wide range of
load currents. Burst Mode operation functions by us-
ing shortburst” cycles to switch the inductor current
through the internal power MOSFET, followed by a sleep
cycle where the power switch is off and the load current is
supplied by the output capacitor. During the sleep cycle,
the LTC3638 draws only 12µA of supply current. At light
loads, the burst cycles are a small percentage of the total
cycle time which minimizes the average supply current,
greatly improving efficiency. Figure 1 shows an example
of Burst Mode operation. The switching frequency is de-
pendent on the inductor value, peak current, input voltage
and output voltage.
External feedback resistors (adjustable mode) can be used
by connecting both VPRG1 and VPRG2 to ground.
In adjustable mode the feedback comparator monitors
the voltage on the VFB pin and compares it to an internal
800mV reference. If this voltage is greater than the refer-
ence, the comparator activates a sleep mode in which
the power switch and current comparators are disabled,
reducing the VIN pin supply current to only 12µA. As the
load current discharges the output capacitor, the voltage
on the VFB pin decreases. When this voltage falls 5mV
below the 800mV reference, the feedback comparator
trips and enables burst cycles.
At the beginning of the burst cycle, the internal high side
power switch (P-channel MOSFET) is turned on and the
inductor current begins to ramp up. The inductor current
increases until either the current exceeds the peak cur-
rent comparator threshold or the voltage on the VFB pin
exceeds 800mV, at which time the switch is turned off
and the inductor current is carried by the external catch
diode. The inductor current ramps down until the switch
node rises, indicating that the current in the catch diode
is zero. If the voltage on the VFB pin is still less than the
800mV reference, the power switch is turned on again and
another cycle commences. The average current during a
burst cycle will normally be greater than the average load
current. For this architecture, the maximum average output
current is equal to half of the peak current.
The hysteretic nature of this control architecture results
in a switching frequency that is a function of the input
voltage, output voltage, and inductor value. This behavior
provides inherent short-circuit protection. If the output is
shorted to ground, the inductor current will decay very
slowly during a single switching cycle. Since the high side
switch turns on only when the inductor current is near
zero, the LTC3638 inherently switches at a lower frequency
during start-up or short-circuit conditions.
BURST
FREQUENCY
INDUCTOR
CURRENT
OUTPUT
VOLTAGE
∆V
OUT 3638 F01
BURST
CYCLE
SLEEP
CYCLE SWITCHING
FREQUENCY
Figure 1. Burst Mode Operation
Main Control Loop
The LTC3638 uses the VPRG1 and VPRG2 control pins to
connect internal feedback resistors to the VFB pin. This
enables fixed outputs of 1.8V, 3.3V or 5V without increas-
ing component count, input supply current or exposure to
noise on the sensitive input to the feedback comparator.
(Refer to Block Diagram)
LTC3638 L7 LJUW 9
LTC3638
9
3638fa
For more information www.linear.com/LTC3638
Start-Up and Shutdown
If the voltage on the RUN pin is less than 0.7V, the LTC3638
enters a shutdown mode in which all internal circuitry is
disabled, reducing the DC supply current to 1.4µA. When the
voltage on the RUN pin exceeds 1.21V, normal operation of
the main control loop is enabled. The RUN pin comparator
has 110mV of internal hysteresis, and therefore must fall
below 1.1V to disable the main control loop.
An internal 1ms soft-start function limits the ramp rate of
the output voltage on start-up to prevent excessive input
supply droop. If a longer ramp time and consequently less
supply droop is desired, a capacitor can be placed from
the SS pin to ground. TheA current that is sourced
out of this pin will create a smooth voltage ramp on the
capacitor. If this ramp rate is slower than the internal 1ms
soft-start, then the output voltage will be limited by the
ramp rate on the SS pin. The internal and external soft-
start functions are reset on start-up, after an undervoltage
or overvoltage event on the input supply, and after an
overtemperature shutdown.
Peak Inductor Current Programming
The peak current comparator nominally limits the peak
inductor current to 575mA. This peak inductor current
can be adjusted by placing a resistor from the ISET pin to
ground. TheA current sourced out of this pin through
the resistor generates a voltage that adjusts the peak cur-
rent comparator threshold.
During sleep mode, the current sourced out of the ISET pin
is reduced toA. The ISET current is increased back toA
on the first switching cycle after exiting sleep mode. The
ISET current reduction in sleep mode, along with adding
a filtering network, RISET and CISET, from the ISET pin to
ground, provides a method of reducing light load output
voltage ripple at the expense of lower efficiency and slightly
degraded load step transient response.
For applications requiring higher output current, the
LTC3638 provides a feedback comparator output pin (FBO)
for combining the output current of multiple LTC3638s.
OPERATION
By connecting the FBO pin of a master LTC3638 to the VFB
pin of one or more slave LTC3638s, the output currents
can be combined to source 250mA times the number of
LTC3638s.
Dropout Operation
When the input supply decreases toward the output sup-
ply, the duty cycle increases to maintain regulation. The
P-channel MOSFET switch in the LTC3638 allows the duty
cycle to increase all the way to 100%. At 100% duty cycle,
the P-channel MOSFET stays on continuously, providing
output current equal to the peak current, which is twice
the maximum load current when not in dropout.
Input Voltage and Overtemperature Protection
When using the LTC3638, care must be taken not to
exceed any of the ratings specified in the Absolute Maxi-
mum Ratings section. As an added safeguard, however,
the LTC3638 incorporates an overtemperature shutdown
feature. If the junction temperature reaches approximately
180°C, the LTC3638 will enter thermal shutdown mode.
The power switch will be turned off and the SW node will
become high impedance. After the part has cooled below
160°C, it will restart. The overtemperature level is not
production tested.
The LTC3638 additionally implements protection features
which inhibit switching when the input voltage is not within
a programmable operating range. By use of a resistive
divider from the input supply to ground, the RUN and
OVLO pins serve as a precise input supply voltage monitor.
Switching is disabled when either the RUN pin falls below
1.1V or the OVLO pin rises above 1.21V, which can be
configured to limit switching to a specific range of input
supply voltage. Furthermore, if the input voltage falls below
3.5V typical (3.8V maximum), an internal undervoltage
detector disables switching.
When switching is disabled, the LTC3638 can safely sustain
input voltages up to the absolute maximum rating of 140V.
Input supply undervoltage or overvoltage events trigger a
soft-start reset, which results in a graceful recovery from
an input supply transient.
(Refer to Block Diagram)
LTC3638 Vow VOUT 600 / CALPEAK 3 ucmn g RENT E g a / / / MAX‘MUM LEAD 7 // CURRENT
LTC3638
10
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
The basic LTC3638 application circuit is shown on the
front page of this data sheet. External component selec-
tion is determined by the maximum load current require-
ment and begins with the selection of the peak current
programming resistor, RISET. The inductor value L can
then be determined, followed by capacitors CIN and COUT.
Peak Current Resistor Selection
The peak current comparator has a maximum current
limit of at least 500mA, which guarantees a maximum
average current of 250mA. For applications that demand
less current, the peak current threshold can be reduced
to as little as 40mA. This lower peak current allows the
efficiency and component selection to be optimized for
lower current applications.
The peak current threshold is linearly proportional to the
voltage on the ISET pin, with 100mV and 1V corresponding
to 40mA and 500mA peak current respectively. This pin
may be driven by an external voltage source to modulate
the peak current, which may be beneficial in some applica-
tions. Usually, the peak current is programmed with an
appropriately chosen resistor (RISET) between the ISET pin
and ground. The voltage generated on the ISET pin by RISET
and the internalA current source sets the peak current.
The value of resistor for a particular peak current can be
computed by using Figure 2 or the following equation:
RISET = IPEAK • 400k
where 40mA < IPEAK < 500mA.
The internalA current source is reduced toA in sleep
mode to maximize efficiency and to facilitate a tradeoff
between efficiency and light load output voltage ripple, as
described in the Optimizing Output Voltage Ripple section.
The peak current is internally limited to be within the range
of 40mA to 500mA. Shorting the ISET pin to ground pro-
grams the current limit to 40mA, and leaving it floating sets
the current limit to the maximum value of 500mA. When
selecting this resistor value, be aware that the maximum
average output current for this architecture is limited to
half of the peak current. Therefore, be sure to select a value
that sets the peak current with enough margin to provide
adequate load current under all conditions. Selecting the
peak current to be 2.2 times greater than the maximum
load current is a good starting point for most applications.
Inductor Selection
The inductor, input voltage, output voltage, and peak current
determine the switching frequency during a burst cycle of
the LTC3638. For a given input voltage, output voltage,
and peak current, the inductor value sets the switching
frequency during a burst cycle when the output is in regu-
lation. Generally, switching at a frequency between 50kHz
and 200kHz yields high efficiency, and 100kHz is a good
first choice for many applications. The inductor value can
be determined by the following equation:
L=VOUT
fIPEAK
1– VOUT
VIN
The variation in switching frequency during a burst cycle
with input voltage and inductance is shown in Figure 3. For
lower values of IPEAK, multiply the frequency in Figure3
by 575mA/IPEAK.
An additional constraint on the inductor value is the
LTC3638’s 150ns minimum on-time of the switch.
Therefore, in order to keep the current in the inductor
well-controlled, the inductor value must be chosen so that
Figure 2. RISET Selection
RISET (kΩ)
0
CURRENT (mA)
200
300
400
500
600
25 75 100 125
3638 F02
100
050 150 175
200
TYPICAL PEAK
INDUCTOR
CURRENT
MAXIMUM
LOAD
CURRENT
LTC3638 ‘50 muuu SWITCHING FREDUENCV (kHz) INDUCTOR VALUE (tu IPEAK L7 LJUW 1 1
LTC3638
11
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
it is larger than a minimum value which can be computed
as follows:
L>
V
IN(MAX)
t
ON(MIN)
I
PEAK
1.2
where VIN(MAX) is the maximum input supply voltage when
switching is enabled, tON(MIN) is 150ns, IPEAK is the peak
current, and the factor of 1.2 accounts for typical inductor
tolerance and variation over temperature.
For applications that have large input supply transients,
the OVLO pin can be used to disable switching above the
maximum operating voltage VIN(MAX) so that the minimum
inductor value is not artificially limited by a transient
condition. Inductor values that violate the above equation
will cause the peak current to overshoot and permanent
damage to the part may occur.
Although the previous equation provides the minimum
inductor value, higher efficiency is generally achieved with
a larger inductor value, which produces a lower switching
frequency. For a given inductor type, however, as induc-
tance is increased DC resistance (DCR) also increases.
Higher DCR translates into higher copper losses and lower
current rating, both of which place an upper limit on the
inductance. The recommended range of inductor values
for small surface mount inductors as a function of peak
current is shown in Figure 4. The values in this range are a
good compromise between the trade-offs discussed above.
For applications where board area is not a limiting factor,
inductors with larger cores can be used, which extends
the recommended range of Figure4 to larger values.
Inductor Core Selection
Once the value for L is known, the type of inductor must
be selected. High efficiency regulators generally cannot
afford the core loss found in low cost powdered iron cores,
forcing the use of the more expensive ferrite cores. Actual
core loss is independent of core size for a fixed inductor
value but is very dependent of the inductance selected.
As the inductance increases, core losses decrease. Un-
fortunately, increased inductance requires more turns of
wire and therefore copper losses will increase.
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing satura-
tion. Ferrite core material saturateshard,” which means
that inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current and consequently output voltage
ripple. Do not allow the core to saturate!
Different core materials and shapes will change the size/
current and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and do not radiate energy but generally cost more
than powdered iron core inductors with similar charac-
teristics. The choice of which style inductor to use mainly
Figure 4. Recommended Inductor Values for Maximum Efficiency
Figure 3. Switching Frequency for VOUT = 3.3V
VIN INPUT VOLTAGE (V)
0
SWITCHING FREQUENCY (kHz)
100
120
160
140
150
120
3638 F03
80
60
030 60 90
40
20
ISET OPEN
L = 47µH
L = 100µH
L = 220µH
PEAK INDUCTOR CURRENT (mA)
10
10
100
INDUCTOR VALUE (µH)
1000
10000
1000
100
3638 F04
LTc3638 fi VIN AVIN M vfl M71 Vom
LTC3638
12
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
depends on the price versus size requirements and any
radiated field/EMI requirements. New designs for surface
mount inductors are available from Coiltronics, Coilcraft,
TDK, Toko, and Sumida.
Catch Diode Selection
The catch diode (D1 from Block Diagram) conducts current
only during the switch off time. Average forward current
in normal operation can be calculated from:
ID(AVG) =IOUT
V
IN
V
OUT
V
IN
where IOUT is the output load current. The maximum av-
erage diode current occurs with a shorted output at the
high line. For this worst-case condition, the diode current
will approach half of the programmed peak current. The
diode reverse voltage rating should be greater than the
maximum operating input voltage. When the OVLO pin is
used to limit the maximum operating input voltage, the
diode reverse voltage should be greater than the OVLO
pin setting, but may be lower the maximum input voltage
during overvoltage lockout.
For high efficiency at full load, it is important to select a
catch diode with a low reverse recovery time and low for-
ward voltage drop. As a result, Schottky diodes are often
used as catch diodes. However, Schottky diodes generally
exhibit much higher leakage than silicon diodes. In sleep,
the catch diode leakage current will appear as load current,
and may significantly reduce light load efficiency. Diodes
with low leakage often have larger forward voltage drops
at a given current, so a trade-off can exist between light
load and full load efficiency.
The selection of Schottky diodes with high reverse voltage
ratings is limited relative to that of silicon diodes. There-
fore, for low reverse leakage and part availability, some
applications may prefer a silicon diode. If a silicon diode
is necessary, be sure to select a diode with a specified low
reverse recovery time to maximize efficiency.
CIN and COUT Selection
The input capacitor, CIN, is needed to filter the trapezoidal
current at the source of the high side MOSFET. CIN should
be sized to provide the energy required to magnetize the
inductor without causing a large decrease in input voltage
(∆VIN). The relationship between CIN andVIN is given by:
CIN >
LI
PEAK2
2V
IN
V
IN
It is recommended to use a larger value for CIN than
calculated by the previous equation since capacitance
decreases with applied voltage. In general, aF X7R ce-
ramic capacitor is a good choice for CIN in most LTC3638
applications.
To prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used. RMS
current is given by:
IRMS =IOUT(MAX) VOUT
VIN
VIN
VOUT
1
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT/2. This simple worst-case condition is commonly used
for design because even significant deviations do not offer
much relief. Note that ripple current ratings from capacitor
manufacturers are often based only on 2000 hours of life
which makes it advisable to further derate the capacitor,
or choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to meet
size or height requirements in the design.
The output capacitor, COUT, filters the inductor’s ripple
current and stores energy to satisfy the load current when
the LTC3638 is in sleep. The output ripple has a lower limit
of VOUT/160 due to the 5mV typical hysteresis of the feed-
back comparator. The time delay of the comparator adds
an additional ripple voltage that is a function of the load
current. During this delay time, the LTC3638 continues to
switch and supply current to the output. The output ripple
LTC3638 IPEAK VOUT PEAK '1 7 IPEAK L7HEJWEGR 1 3
LTC3638
13
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
can be approximated by:
VOUT IPEAK
2ILOAD
4106
COUT
+VOUT
160
The output ripple is a maximum at no load and approaches
lower limit of VOUT/160 at full load. Choose the output
capacitor COUT to limit the output voltage rippleVOUT
using the following equation:
COUT IPEAK 2106
VOUT VOUT
160
The value of the output capacitor must also be large enough
to accept the energy stored in the inductor without a large
change in output voltage during a single switching cycle.
Setting this voltage step equal to 1% of the output voltage,
the output capacitor must be:
COUT >L
2IPEAK
VOUT
2
100%
1%
Typically, a capacitor that satisfies the voltage ripple re-
quirement is adequate to filter the inductor ripple. To avoid
overheating, the output capacitor must also be sized to
handle the ripple current generated by the inductor. The
worst-case ripple current in the output capacitor is given
by IRMS = IPEAK/2. Multiple capacitors placed in parallel
may be needed to meet the ESR and RMS current handling
requirements.
Dry tantalum, special polymer, aluminum electrolytic,
and ceramic capacitors are all available in surface mount
packages. Special polymer capacitors offer very low ESR
but have lower capacitance density than other types.
Tantalum capacitors have the highest capacitance density
but it is important only to use types that have been surge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have significantly higher ESR but
can be used in cost-sensitive applications provided that
consideration is given to ripple current ratings and long-
term reliability. Ceramic capacitors have excellent low ESR
characteristics but can have high voltage coefficient and
audible piezoelectric effects. The high quality factor (Q)
of ceramic capacitors in series with trace inductance can
also lead to significant input voltage ringing.
Input Voltage Steps
If the input voltage falls below the regulated output voltage,
the body diode of the internal MOSFET will conduct current
from the output supply to the input supply. If the input
voltage falls rapidly, the voltage across the inductor will be
significant and may saturate the inductor. A large current
will then flow through the MOSFET body diode, resulting
in excessive power dissipation that may damage the part.
If rapid voltage steps are expected on the input supply, put
a small silicon or Schottky diode in series with the VIN pin
to prevent reverse current and inductor saturation, shown
below as D1 in Figure 5. The diode should be sized for a
reverse voltage of greater than the regulated output volt-
age, and to withstand repetitive currents higher than the
maximum peak current of the LTC3638.
Figure 5. Preventing Current Flow to the Input
SW
INPUT
SUPPLY
LTC3638
COUT
3638 F05
CIN
V
OUT
VIN L
D1
Ceramic Capacitors and Audible Noise
Higher value, lower cost ceramic capacitors are now be-
coming available in smaller case sizes. Their high ripple
current, high voltage rating, and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
LTc3638
LTC3638
14
3638fa
For more information www.linear.com/LTC3638
VFB
V
OUT
R2
3638 F07
0.8V R1
VPRG1
VPRG2
LTC3638
Figure 7. Setting the Output Voltage with External Resistors
APPLICATIONS INFORMATION
the power is supplied by a wall adapter through long wires,
a load step at the output can induce ringing at the input,
VIN. At best, this ringing can couple to the output and be
mistaken as loop instability. At worst, a sudden inrush
of current through the long wires can potentially cause
a voltage spike at VIN large enough to damage the part.
For applications with inductive source impedance, such
as a long wire, a series RC network may be required in
parallel with CIN to dampen the ringing of the input supply.
Figure 6 shows this circuit and the typical values required
to dampen the ringing. Refer to Application Note 88 for ad-
ditional information on suppressing input supply transients.
Ceramic capacitors are also piezoelectric. The LTC3638’s
burst frequency depends on the load current, and in some
applications the LTC3638 can excite the ceramic capaci-
tor at audio frequencies, generating audible noise. This
noise is typically very quiet to a casual ear; however, if the
noise is unacceptable, use a high performance tantalum
or electrolytic capacitor at the output.
Output Voltage Programming
The LTC3638 has three fixed output voltage modes and
an adjustable mode that can be selected with the VPRG1
and VPRG2 pins. The fixed output modes use an internal
feedback divider which enables higher efficiency, higher
noise immunity, and lower output voltage ripple for 5V,
3.3V, and 1.8V applications. To select the fixed 5V output
voltage, connect VPRG1 to SS and VPRG2 to GND. For 3.3V,
connect VPRG1 to GND and VPRG2 to SS. For 1.8V, connect
both VPRG1 and VPRG2 to SS. For any of the fixed output
voltage options, directly connect the VFB pin to VOUT.
For the adjustable output mode (VPRG1 = VPRG2 = GND),
the output voltage is set by an external resistive divider
according to the following equation:
VOUT =0.8V • 1+
R1
R2
The resistive divider allows the VFB pin to sense a fraction
of the output voltage as shown in Figure 7. The output
voltage can range from 0.8V to VIN. Be careful to keep
the divider resistors very close to the VFB pin to minimize
noise pick-up on the sensitive VFB trace.
R=LIN
CIN
4 • CIN
CIN
LIN
3638
F06
VIN
LTC3638
Figure 6. Series RC to Reduce VIN Ringing
To minimize the no-load supply current, resistor values in
the megohm range may be used; however, large resistor
values should be used with caution. The feedback divider
is the only load current when in shutdown. If PCB leakage
current to the output node or switch node exceeds the load
current, the output voltage will be pulled up. In normal
operation, this is generally a minor concern since the load
current is much greater than the leakage.
To avoid excessively large values of R1 in high output volt-
age applications (VOUT ≥ 10V), a combination of external
and internal resistors can be used to set the output volt-
age. This has an additional benefit of increasing the noise
LTC3638 ..,J u 1.21V L7Hߤ0g 1 5
LTC3638
15
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
The RUN and OVLO pins can alternatively be configured
as precise undervoltage (UVLO) and overvoltage (OVLO)
lockouts on the VIN supply with a resistive divider from VIN
to ground. A simple resistive divider can be used as shown
in Figure 10 to meet specific VIN voltage requirements.
4.2M
R1
5V
R2
3638 F08
V
OUT
800k
0.8V
VFB
SS
VPRG1
VPRG2
LTC3638
Figure 8. Setting the Output Voltage with
External and Internal Resistors
RUN
SUPPLY LTC3638
RUN
3638
F09
4.7M
1k
V
IN
LTC3638
1k
Figure 9. RUN Pin Interface to Logic
Figure 10. Adjustable UV and OV Lockout
RUN
3638
F10
R3
V
IN
LTC3638
R4
R5
OVLO
immunity on the VFB pin. Figure 8 shows the LTC3638
with the VFB pin configured for a 5V fixed output with an
external divider to generate a higher output voltage. The
internal 5M resistance appears in parallel with R2, and
the value of R2 must be adjusted accordingly. R2 should
be chosen to be less than 200k to keep the output volt-
age variation less than 1% due to the tolerance of the
LTC3638’s internal resistor.
The current that flows through the R3-R4-R5 divider will
directly add to the shutdown, sleep, and active current of
the LTC3638, and care should be taken to minimize the
impact of this current on the overall efficiency of the ap-
plication circuit. Resistor values in the megohm range may
be required to keep the impact on quiescent shutdown and
sleep currents low. To pick resistor values, the sum total
of R3 + R4 + R5 (RTOTAL) should be chosen first based
on the allowable DC current that can be drawn from VIN.
The individual values of R3, R4 and R5 can then be cal-
culated from the following equations:
R5=RTOTAL
1.21V
Rising VIN OVLO Threshold
R4=RTOTAL 1.21V
Rising VIN UVLO Threshold R5
R3=RTOTAL R5R4
For applications that do not need a precise external OVLO,
the OVLO pin should be tied directly to ground. The RUN
pin in this type of application can be used as an external
UVLO using the previous equations with R5 = 0Ω.
RUN Pin and Overvoltage/Undervoltage Lockout
The LTC3638 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3638 into a low quiescent current shutdown mode
(IQ ~ 1.4µA). When the RUN pin is greater than 1.21V,
switching is enabled. Figure 9 shows examples of con-
figurations for driving the RUN pin from logic.
LTc3638 200m IPEAK w 0.8V
LTC3638
16
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
Similarly, for applications that do not require a precise
UVLO, the RUN pin can be tied to VIN. In this configuration,
the UVLO threshold is limited to the internal VIN UVLO
thresholds as shown in the Electrical Characteristics table.
The resistor values for the OVLO can be computed using
the previous equations with R3 = 0Ω.
Be aware that the OVLO pin cannot be allowed to exceed
its absolute maximum rating of 6V. To keep the voltage
on the OVLO pin from exceeding 6V, the following relation
should be satisfied:
VIN(MAX)
R5
R3+R4+R5
<6V
If this equation cannot be satisfied in the application,
connect a 4.7V Zener diode between the OVLO pin and
ground to clamp the OVLO pin voltage.
Soft-Start
Soft-start is implemented by ramping the effective refer-
ence voltage from 0V to 0.8V. To increase the duration of
the soft-start, place a capacitor from the SS pin to ground.
An internalA pull-up current will charge this capacitor.
The value of the soft-start capacitor can be calculated by
the following equation:
CSS =Soft-Start Time •
5µA
0.8V
The minimum soft-start time is limited to the internal
soft-start timer of 1ms. When the LTC3638 detects a
fault condition (input supply undervoltage/overvoltage or
overtemperature) or when the RUN pin falls below 1.1V,
the SS pin is quickly pulled to ground and the internal
soft-start timer is reset. This ensures an orderly restart
when using an external soft-start capacitor.
Note that the soft-start capacitor may not be the limiting
factor in the output voltage ramp. The maximum output
current, which is equal to half of the peak current, must
charge the output capacitor from 0V to its regulated value.
For small peak currents or large output capacitors, this
ramp time can be significant. Therefore, the output voltage
ramp time from 0V to the regulated VOUT value is limited
to a minimum of
Ramp Time
2C
OUT
I
PEAK
VOUT
Optimizing Output Voltage Ripple
After the peak current resistor and inductor have been
selected to meet the load current and frequency require-
ments, an optional capacitor, CISET can be added in parallel
with RISET to reduce the output voltage ripple dependency
on load current.
At light loads the output voltage ripple will be a maximum.
The peak inductor current is controlled by the voltage on
the ISET pin. The current out of the ISET pin isA while
the LTC3638 is active and is reduced toA during sleep
mode. The ISET current will return toA on the first
switching cycle after sleep mode. Placing a parallel RC
network to ground on the ISET pin filters the ISET voltage
as the LTC3638 enters and exits sleep mode, which in
turn will affect the output voltage ripple, efficiency, and
load step transient performance.
Higher Current Applications
For applications that require more than 250mA, the
LTC3638 provides a feedback comparator output pin
(FBO) for driving additional LTC3638s. When the FBO pin
of a master LTC3638 is connected to the VFB pin of one
or more slave LTC3638s, the master controls the burst
cycle of the slaves.
Figure 11 shows an example of a 5V, 500mA regulator
using two LTC3638s. The master is configured for a 5V
fixed output with external soft-start and VIN UVLO/OVLO
levels set by the RUN and OVLO pins. Since the slave is
directly controlled by the master, its SS pin should be
floating, RUN should be tied to VIN, and OVLO should be
tied to ground. Furthermore, the slave should be configured
for a 1.8V fixed output (VPRG1 = VPRG2 = SS) to set the
LTC3638 .||—| L7Hfl§0g 1 7
LTC3638
17
3638fa
For more information www.linear.com/LTC3638
VFB
SW
L1
L2
VIN
RUN
R3
CIN COUT
V
OUT
5V
500mA
CSS
V
IN
R4
R5
OVLO
SS
VPRG1
VPRG2
FBO
LTC3638
(MASTER)
SW
VFB
VIN
RUN
OVLO
SS
VPRG1
VPRG2
FBO
3638 F11
LTC3638
(SLAVE)
D2
D1
Figure 11. 5V, 500mA Regulator
APPLICATIONS INFORMATION
The junction temperature is given by:
TJ = TA + TR
Generally, the worst-case power dissipation is in dropout
at low input voltage. In dropout, the LTC3638 can provide
a DC current as high as the full 575mA peak current to the
output. At low input voltage, this current flows through a
higher resistance MOSFET, which dissipates more power.
As an example, consider the LTC3638 in dropout at an input
voltage of 5V, a load current of 575mA and an ambient
temperature of 85°C. From the Typical Performance graphs
of Switch On-Resistance, the RDS(ON) of the top switch
at VIN = 5V and 100°C is approximately 3.2Ω. Therefore,
the power dissipated by the part is:
PD = (ILOAD)2 • RDS(ON) = (575mA)2 • 3.2Ω = 1.06W
For the MSOP package the θJA is 40°C/W. Thus, the junc-
tion temperature of the regulator is:
TJ=85°C+1.06W
40°C
W
=127°C
which is below the maximum junction temperature of
150°C.
Note that the while the LTC3638 is in dropout, it can provide
output current that is equal to the peak current of the part.
This can increase the chip power dissipation dramatically
and may cause the internal overtemperature protection
circuitry to trigger at 180°C and shut down the LTC3638.
Pin Clearance/Creepage Considerations
The LTC3638 MSE package has been uniquely designed to
meet high voltage clearance and creepage requirements.
Pins 2, 4, 13, and 15 are omitted to increase the spac-
ing between adjacent high voltage solder pads (VIN, SW,
and RUN) to a minimum of 0.657mm which is sufficient
for most applications. For more information, refer to the
printed circuit board design standards described in IPC-
2221 (www.ipc.org).
VFB pin threshold at 1.8V. The inductors L1 and L2 do not
necessarily have to be the same, but should both meet
the criteria described in the Inductor Selection section.
Thermal Considerations
In most applications, the LTC3638 does not dissipate much
heat due to its high efficiency. But, in applications where
the LTC3638 is running at high ambient temperature with
low supply voltage and high duty cycles, such as dropout,
the heat dissipated may exceed the maximum junction
temperature of the part.
To prevent the LTC3638 from exceeding the maximum
junction temperature, the user will need to do some thermal
analysis. The goal of the thermal analysis is to determine
whether the power dissipated exceeds the maximum junc-
tion temperature of the part. The temperature rise from
ambient to junction is given by:
TR = PDθJA
Where PD is the power dissipated by the regulator and
θJA is the thermal resistance from the junction of the die
to the ambient temperature.
LTC3638 90V'150ns 0.575A fl, 12V 90V712V 90V '10 E 160 120mV 0.575A 12V75V 5V 18 L7LJCUEN2
LTC3638
18
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
Design Example
As a design example, consider using the LTC3638 in an
application with the following specifications: VIN = 36V
to 72V (48V nominal), VOUT = 12V, IOUT = 250mA, f =
200kHz, and that switching is enabled when VIN is between
30V and 90V.
First, calculate the inductor value based on the switching
frequency:
L=
12V
200kHz •0.575A
• 1–
12V
48V
78µH
Choose a 100µH inductor as a standard value. Next, verify
that this meets the LMIN requirement at the maximum
input voltage:
LMIN =
90V 150ns
0.575A
1.2=28µH
Therefore, the minimum inductor requirement is satisfied
and the 100μH inductor value may be used.
Next, CIN and COUT are selected. For this design, CIN should
be sized for a current rating of at least:
IRMS =250mA • 12V
36V
36V
12V
1118mARMS
The value of CIN is selected to keep the input from droop-
ing less than 360mV (1%) at low line:
CIN >100µH0.575A2
236V •360mV
1.3µF
Since the capacitance of capacitors decreases with DC
bias, a 2.2µF capacitor should be chosen.
The catch diode should have a reverse voltage rating of
greater than the overvoltage lockout setting of 90V. It should
also be rated for an average forward current of at least:
ID(AVG) =250mA
90V 12V
90V
=217mA
During a short-circuit, the average current in the diode
could be as high as IPEAK/2, or 288mA. For margin, select
a catch diode with a reverse breakdown of at least 100V
and an average current of 350mA or higher.
COUT will be selected based on a value large enough to
satisfy the output voltage ripple requirement. For a 1%
output ripple (120mV), the value of the output capacitor
can be calculated from:
COUT 0.575A •2106
120mV – 12V
160
26µF
COUT also needs an ESR that will satisfy the output voltage
ripple requirement. The required ESR can be calculated
from:
ESR<
120mV
0.575A
208m
A 33µF ceramic capacitor has significantly less ESR than
208mΩ. The output voltage can now be programmed by
choosing the values of R1 and R2. Since the output volt-
age is higher than 10V, the LTC3638 should be set for a
5V fixed output with an external divider to divide the 12V
output down to 5V. R2 is chosen to be less than 200k
to keep the output voltage variation to less than 1% due
to the internal 5M resistor tolerance. Set R2 = 196k and
calculate R1 as:
R1=
12V 5V
5V
• 196k5M
( )
=264k
Choose a standard value of 267k for R1.
1.21V02.5MQ R3:2.5MQ*R47R5: 2.4M || H r. || || L7 LJUW LTC3638 19
LTC3638
19
3638fa
For more information www.linear.com/LTC3638
APPLICATIONS INFORMATION
The undervoltage and overvoltage lockout requirements
on VIN can be satisfied with a resistive divider from VIN to
the RUN and OVLO pins (refer to Figure 10). Choose R3 +
R4 + R5 = 2.5M to minimize the loading on VIN. Calculate
R3, R4 and R5 as follows:
R5=
1.21V 2.5M
VIN _OV(RISING)
=33.6k
R4=1.21V •2.5M
VIN_UV(RISING)
R5=67.2k
R3=2.5MR4R5=2.4M
Since specific resistor values in the megohm range are
generally less available, it may be necessary to scale R3,
R4, and R5 to a standard value of R3. For this example,
choose R3 = 2.2M and scale R4 and R5 by 2.2M/2.4M.
Then, R4 = 61.6k and R5 = 30.8k. Choose standard values
of R3 = 2.2M, R4 = 62k, and R5 = 30.9k. Note that the fall-
ing thresholds for both UVLO and OVLO will be 10% less
than the rising thresholds, or 27V and 81V respectively.
The ISET pin should be left open in this example to select
maximum peak current (575mA). Figure 12 shows a
complete schematic for this design example.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3638. Check the following in your layout:
1. Large switched currents flow in the power switch, catch
diode, and input capacitor. The loop formed by these
components should be as small as possible. A ground
plane is recommended to minimize ground impedance.
2. Connect the (+) terminal of the input capacitor, CIN, as
close as possible to the VIN pin. This capacitor provides
the AC current into the internal power MOSFET.
3. Keep the switching node, SW, away from all sensitive
small signal nodes. The rapid transitions on the switching
node can couple to high impedance nodes, in particular
VFB, and create increased output ripple.
3638 F12
VFB
ISET
FBO
SW
100µH
VIN
RUN
2.2M 267k
196k
2.2µF 33µF
VOUT
12V
250mA
VIN
36V TO 72V
62k
30.9k
OVLO
VPRG2
LTC3638
SS
VPRG1
GND
Figure 12. 36V to 72V Input to 12V Output, 250mA Regulator
VFB
ISET
SW
L1
VIN
RUN
R3 R1
D1
R2
CIN COUT
V
OUT
V
IN
R4
RISET
R5
OVLO
VPRG1
SS
VPRG2
LTC3638
GND
FBO
CSS
3638 F13
COUT
VOUT
VIN
GND
GND
R3
RISET
CSS
R5
VIAS TO GROUND PLANE
VIAS TO INPUT SUPPLY (VIN)
VIAS TO OUTPUT SUPPLY (VOUT)
OUTLINE OF LOCAL GROUND PLANE
R4
R1R2
L1
CIN
D1
Figure 13. Example PCB Layout
LTC3638 U ‘00 NA :: E 5 U 1 l— A U 250 \ 5v /—’-—-— ‘E / /’ 5 g / VuuTV‘iV % I: 3 q 8 / E E E / g C‘ KEMETCZZZSCWSKAR mum» cm AVX umacmsmm U TDK smzassqma m ST NHCRO swam 20 L7ELUEN2
LTC3638
20
3638fa
For more information www.linear.com/LTC3638
VIN INPUT VOLTAGE (V)
0
EFFICIENCY (%)
85
90
100
95
150
120
3638 F14b
80
75
60 30 60 90
70
65
IOUT = 100mA
VOUT = 5V
VOUT = 3.3V
VOUT = 1.8V
VIN INPUT VOLTAGE (V)
0
MAXIMUM LOAD CURRENT (mA)
250
200
150
100
150
120
3638 TA04b
50 30 60 90
VOUT = –5V
VOUT = –15V
OUTPUT
VOLTAGE
500mV/DIV
10ms/DIV
3638
F15b
30Ω LOAD
CIN: TDK C5750X7R2E105K
COUT: TDK C3216X5R0J226MT
L1: COILCRAFT MSS1278T-334KL
D1: DIODES INC PDS3200
*VOUT = VIN FOR VIN < 5V
3638 F14
VFB
ISET
SW
L1
330µH
VIN
RUN
CIN
F
250V
COUT
22µF
VOUT*
5V
250mA
VIN
4V TO 140V
SS
OVLOVPRG1
VPRG2
LTC3638
GND
FBO
D1
Efficiency vs Input Voltage
TYPICAL APPLICATIONS
4V to 125V Input to –15V Output Positive-to-Negative Regulator
3638 F15
VFB
SS
SW
L1
68µH
VIN
RUN
CIN
F
250V
COUT
100µF
VOUT*
3.3V
250mA
VIN
4V TO 140V
ISET
VPRG2
VPRG1
OVLO
LTC3638
GND
FBO
470nF
D1
220pF
CIN: MURATA GRM55DR72E105KW01L
COUT: MURATA GRM43SR60J107ME20
L1: SUMIDA CDRH8D28NP-680NC
D1: VISHAY U1D
220k
3638
TA04a
VFB
ISET
SW
L1
220µH
VIN
RUN
CIN
F
250V
COUT
10µF
25V
V
OUT
–15V
VIN
4V TO 125V
SS
OVLOVPRG1
VPRG2
LTC3638
GND
FBO
200k
102k
MAXIMUM LOAD CURRENT
V
IN
VIN +VOUT
I
PEAK
2
D1
MAXIMUM INPUT VOLTAGE = 140 –|VOUT|
CIN: KEMET C2225C105KARACTU
COUT: AVX 12103C106MAT
L1: TDK SLF12555-221MR72
D1: ST MICRO STTH102A
Soft-Start Waveform
Maximum Load Current
vs Input Voltage
Figure 14. High Efficiency 250mA Regulator
Figure 15. Low Output Voltage Ripple 250mA Regulator with 75ms Soft-Start
LTC3638 | |_| zoom/u w L7 LJUW 2 1
LTC3638
21
3638fa
For more information www.linear.com/LTC3638
L1 CURRENT
500mA/DIV
VIN/VOUT
5V/DIV
L2 CURRENT
500mA/DIV
1s/DIV
3638
TA05b
VIN
VOUT
L1 CURRENT
500mA/DIV
VIN
50V/DIV
VOUT
10V/DIV
L2 CURRENT
500mA/DIV
200ms/DIV
3638
TA05c
TRANSIENT TO 140V
72V
Low Dropout Startup and
Shutdown
Overvoltage Lockout Operation
TYPICAL APPLICATIONS
3638 TA05a
VFB
ISET
SW
L1
47µH
VIN
RUN
CIN1
F
200V
CIN2
F
200V
COUT
47µF
16V
X5R
VOUT*
12V
500mA
VIN
4V TO 90V
UP TO 140V
TRANSIENT
SS
FBOVPRG1
VPRG2
OVLO
LTC3638
(MASTER)
GND
VFB
ISET
SW
L2
47µH
VIN
RUN
SS
FBOVPRG2
VPRG1
OVLO
LTC3638
(SLAVE)
GND
1M
13.7k
267k
196k
CIN1/CIN2: VISHAY VJ2225Y105KXCA
COUT: TAIYO YUDEN EMK325 BJ 476MM-T
L1/L2: WÜRTH 744 778 914 7
D1/D2: CENTRAL SEMI CMSH1-100M-LTN
*V
OUT
= V
IN
FOR V
IN
< 12V
D1
D2
4V to 90V Input to 12V/500mA Output Regulator with Overvoltage Lockout
LTC3638 c‘ TDK 05750X7R2E cw TDK 045mm u TDK smmam m TosmBAanm NH VISHAY squole $035505 mu E 300 MAXIMUM CURRENT (mA) 7 MAX‘MUM LOAD CURRENT MUMIN PUT CUR L7LJCUEN2
LTC3638
22
3638fa
For more information www.linear.com/LTC3638
TYPICAL APPLICATIONS
36V to 140V to 36V/250mA with 75mA Input Current Limit
CIN: TDK C5750X7R2E105K
COUT: TDK C4532X7R1H475M
L1: TDK SLF12555T-101M1R1
D1: ROHM RF101L2S
3638 TA06a
VFB
SS
SW
L1
100µH
VIN
RUN
CIN
F
250V
COUT
4.7µF
50V
VOUT
36V
250mA*
VIN
36V TO 140V
ISET
OVLO
LTC3638
GND
FBO
220k
35.7k
R1
470k
R2
4.02k
VPRG1
VPRG2
INPUT CURRENT LIMIT =VOUT
4R2
R1+R2 1+5µA R1
VIN
VOUT
4R2
R1+R2
*MAXIMUM LOAD CURRENT =VIN
36V
75mA 250mA
D1
Maximum Load and Input Current
vs Input Voltage
VIN INPUT VOLTAGE (V)
40
MAXIMUM CURRENT (mA)
200
250
300
150
140130120110
3638 TA06b
150
0
50
50 807060 10090
100
MAXIMUM LOAD CURRENT
MAXIMUM INPUT CURRENT
VIN INPUT VOLTAGE (V)
30
EFFICIENCY (%)
85
90
100
95
150
120
3638 TA03b
80 60 90
PWM OPEN
VDIM OPEN
6W LED Driver
3638 TA03a
VFB
OVLO
SW
L1
100µH
VIN
CIN
F
250V
COUT
4.7µF
50V
VOUT
M1
24V LED
250mA
VIN
32V TO 140V
FBO
VPRG2
ISET
VDIM VPRG1
SS
RUN
LTC3638
GND
1M
42.2k
1M
27.4k
3.3V
PWM
CIN: TDK C5750X7R2E105K
COUT: TDK C4532X7R1H475M
L1: TDK SLF10145T-101M
D1: TOSHIBA CRH01
M1: VISHAY SILICONIX Si2356DS
VDIM = 0.1V TO 1V FOR 10:1 ANALOG DIMMING
PWM = SQUARE WAVE FOR DIGITAL DIMMING
30V OVERVOLTAGE PROTECTION ON VOUT
D1
Efficiency vs Input Voltage
LTC3638 mu EURSTFREUUENCV (kHz) HI— . ,H; Em mu INPUT CURRENTWA) L7HEJWEGR 23
LTC3638
23
3638fa
For more information www.linear.com/LTC3638
5V to 140V Input to 5V/250mA Output with 20kHz Minimum Burst Frequency
Input Current vs Load Current
Burst Frequency vs Load Current
3638 TA08a
VFB
SW
L1
100µH
VIN
RUN
CIN
F
250V
COUT
22µF
VOUT
5V
250mA
VIN
5V TO 140V
VPRG1
VPRG2
OVLO
LTC3638
GND
ISET FBO
SS
953k 10Ω
2N7000
100k 200k
OUT
SET
V+
IN
DIV
LTC6994-1
GND
CIN: AVX 2225PC105MAT1A
COUT: KEMET C1206C226K9PAC
L1: COILTRONICS DR74-101-R
D1: DIODES INC MURS120-13-F
D1 0.1 100
1000
101
LOAD CURRENT (mA)
BURST FREQUENCY (kHz)
100
1
10
3638 TA08b
0.01
0.1 WITHOUT BURST FREQUENCY LIMIT
WITH BURST FREQUENCY LIMIT
VIN = 48V
0.1 100
1000
101
LOAD CURRENT (mA)
INPUT CURRENT (mA)
100
1
10
3638 TA08c
0.01
0.1 WITHOUT BURST FREQUENCY LIMIT
WITH BURST FREQUENCY LIMIT
VIN = 48V
TYPICAL APPLICATIONS
LTc3638 msE PamkaaE was :n ‘27 <_. [035="" :uufi)="" m="" n="" pnmfi="" 3207345="" 12w="" 77+7,7m="" 0="" ans="" :n="" 038="" a="" ‘e="" e="" (mu="" :umfi)="" +="" (my)="" fififegfij‘="" ,="" fifiié¢="" +="" ,7“="" o="" \="" 1—,flii="" ,qume="" a="" ,4l_,="" t122%i)="" jehme*="" 1’7="" mm="" 79‘="" ‘9="" ‘="" dimens="" 2="" draw‘="" 3="" dimen="" mold="" a="" dime="" \nte="" 5="" lea="" 5="" ex="" n="">
LTC3638
24
3638fa
For more information www.linear.com/LTC3638
MSOP (MSE16(12)) 0213 REV D
0.53 ±0.152
(.021 ±.006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 –0.27
(.007 – .011)
TYP
0.86
(.034)
REF
0.50
(.0197)
BSC
1.0
(.039)
BSC
1.0
(.039)
BSC
16
16 14 121110
1 3 5 6 7 8
9
9
18
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ±0.127
(.035 ±.005)
RECOMMENDED SOLDER PAD LAYOUT
0.305 ±0.038
(.0120
±.0015)
TYP
0.50
(.0197)
BSC
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
2.845 ±0.102
(.112 ±.004)
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102
(.065 ±.004)
0.1016 ±0.0508
(.004 ±.002)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
0.280 ±0.076
(.011 ±.003)
REF
4.90 ±0.152
(.193 ±.006)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.12 REF
0.35
REF
MSE Package
Variation: MSE16 (12)
16-Lead Plastic MSOP with 4 Pins Removed
Exposed Die Pad
(Reference LTC DWG # 05-08-1871 Rev D)
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC3638 L7Hߤ0g 25
LTC3638
25
3638fa
For more information www.linear.com/LTC3638
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.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 12/14 Clarified OVLO Pin Function
Clarified Related Parts List
6
24
LTC3638 mu — A :: _ :: g E I: <3? g="" g="" e="" _="" _‘="" e="" is="" .||—o—="">
LTC3638
26
3638fa
For more information www.linear.com/LTC3638
LINEAR TECHNOLOGY CORPORATION 2014
LT 1214 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC3638
RELATED PARTS
TYPICAL APPLICATION
12V/250mA Automotive Supply
*VOUT = VIN FOR VIN < 12V
VOUT
12V*
250mA
3638 TA07
VFB
ISET
SW
L1
220µH
VIN
RUN
CIN
F
250V
X7R
COUT
10µF
16V
X7R
VIN
4V TO 140V
SS
OVLOVPRG1
VPRG2
LTC3638
GND
FBO
267k
196k
D1
L1: COILCRAFT MSS1246T-224KL
D1: DIODES INC SBR1U200P1-7
PART NUMBER DESCRIPTION COMMENTS
LTC7138 140V, 400mA Micropower Step-Down Regulator VIN: 4V to 140V, VOUT(MIN) = 0.8V, IQ = 12μA, ISD = 1.4μA, MSE16 Package
LTC3639 150V, 100mA Synchronous Micropower Step-Down
DC/DC Regulator VIN: 4V to 150V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD = 1.4µA, MS16E Package
LTC3630 65V, 500mA Synchronous Step-Down DC/DC
Regulator VIN: 4V to 65V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD = 5µA,
3mm × 5mm DFN16, MSOP16E Packages
LTC3637 76V, 1A Synchronous Step-Down DC/DC Regulator VIN: 4V to 76V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD = 3µA,
3mm × 5mm DFN16, MSOP16E Packages
LTC3630A 76V, 500mA Synchronous Step-Down DC/DC
Regulator VIN: 4V to 76V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD = 5µA,
3mm × 5mm DFN16, MSOP16E Packages
LTC3810 100V Synchronous Step-Down DC/DC Controller VIN: 6.4V to 100V, VOUT(MIN) = 0.8V, IQ = 2mA, ISD < 240µA,
SSOP28 Package
LTC3631/LTC3631-
3.3 LTC3631-5 45V (Transient to 60V), 100mA Synchronous Step-
Down DC/DC Regulator VIN: 4.5V to 45V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD < 3µA,
3mm × 3mm DFN8, MSOP8 Packages
LTC3642 45V (Transient to 60V), 50mA Synchronous Step-
Down DC/DC Regulator VIN: 4.5V to 45V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD < 3µA,
3mm × 3mm DFN8, MSOP8 Packages
LTC3632 50V (Transient to 60V), 20mA Synchronous Step-
Down DC/DC Regulator VIN: 4.5V to 45V, VOUT(MIN) = 0.8V, IQ = 12µA, ISD < 3µA,
3mm × 3mm DFN8, MSOP8 Packages
LTC3891 60V Synchronous Step-Down DC/DC Controller with
Burst Mode Operation VIN: 4V to 60V, VOUT(MIN) = 0.8V, IQ = 50µA, ISD < 14µA,
3mm × 4mm QFN20, TSSOP20E Packages
Efficiency and Power Loss vs
Load Current
VIN = 24V
VIN = 48V
VIN = 120V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
POWER LOSS (mW)
90
100
20
10
80
50
70
10
1
100
60
40
3638 TA07b
0
EFFICIENCY
POWER LOSS
1000
0.1 100 1000101

Products related to this Datasheet

IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
LTC3638 DEMO BOARD - 4V TO 140V
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP
IC REG BUCK ADJ 250MA 16MSOP