LTC3638
High Efficiency, 140V
250mA Step-Down
Regulator
FEATURES
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DESCRIPTION
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, LTC, LTM, 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.
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Wide Operating Input Voltage Range: 4V to 140V
Internal Low Resistance Power MOSFET
No Compensation Required
Adjustable 20mA to 250mA Maximum Output
Current
Low Dropout Operation: 100% Duty Cycle
Low Quiescent Current: 12µA
Wide Output Range: 0.8V to V
IN
0.8V ±1% Feedback Voltage Reference
Precise RUN Pin Threshold
Internal or External Soft-Start
Programmable 1.8V, 3.3V, 5V or Adjustable Output
Few External Components Required
Programmable Input Overvoltage Lockout
Thermally Enhanced High Voltage MSOP Package
APPLICATIONS
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Industrial Control Supplies
Medical Devices
Distributed Power Systems
Portable Instruments
Battery-Operated Devices
Avionics
Automotive
TYPICAL APPLICATION
5V to 140V Input to 5V Output, 250mA Step-Down Regulator
V
IN
5V TO 140V
C
IN
1µF
250V
L1
220µH
V
IN
LTC3638
RUN
V
FB
C
OUT
22µF
SW
V
OUT
5V
250mA
Efficiency and Power Loss vs Load Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
3638 TA01a
EFFICIENCY
V
IN
= 12V
V
IN
= 48V
V
IN
= 140V
POWER LOSS (mW)
1000
100
10
OVLO
SS
V
PRG1
V
PRG2
GND
POWER LOSS
0
0.1
1
10
100
LOAD CURRENT (mA)
1
1000
3638 TA01b
3638fa
For more information
www.linear.com/LTC3638
1
LTC3638
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SW 1
V
IN
3
FBO
V
PRG2
V
PRG1
GND
5
6
7
8
17
GND
16 GND
14 RUN
12
11
10
9
OVLO
I
SET
SS
V
FB
V
IN
Supply Voltage ................................... –0.3V to 140V
RUN Voltage............................................. –0.3V to 140V
SS, FBO, OVLO, I
SET
Voltages ...................... –0.3V to 6V
V
FB
, V
PRG1
, V
PRG2
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 ....................................... –55°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
MSE PACKAGE
VARIATION: MSE16 (12)
16-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3638EMSE#PBF
LTC3638IMSE#PBF
LTC3638HMSE#PBF
LTC3638MPMSE#PBF
TAPE AND REEL
LTC3638EMSE#TRPBF
LTC3638IMSE#TRPBF
LTC3638HMSE#TRPBF
LTC3638MPMSE#TRPBF
PART MARKING*
3638
3638
3638
3638
PACKAGE DESCRIPTION
16-Lead Plastic MSOP
16-Lead Plastic MSOP
16-Lead Plastic MSOP
16-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–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/
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, unless otherwise noted.
SYMBOL
V
IN
V
OUT
UVLO
PARAMETER
Input Voltage Operating Range
Output Voltage Operating Range
V
IN
Undervoltage Lockout
DC Supply Current (Note 5)
Active Mode
Sleep Mode
Shutdown Mode
RUN Pin Threshold
V
IN
Rising
V
IN
Falling
Hysteresis
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ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
4
0.8
3.5
3.3
TYP
MAX
140
V
IN
UNITS
V
V
V
V
mV
µA
µA
µA
V
V
mV
nA
V
V
mV
3638fa
Input Supply (V
IN
)
3.75
3.5
250
150
12
1.4
4.0
3.8
I
Q
No Load
V
RUN
= 0V
RUN Rising
RUN Falling
Hysteresis
RUN = 1.3V
OVLO Rising
OVLO Falling
Hysteresis
1.17
1.06
–10
1.17
1.06
350
22
6
1.25
1.14
10
1.25
1.14
V
RUN
I
RUN
V
OVLO
1.21
1.10
110
0
1.21
1.10
110
RUN Pin Leakage Current
OVLO Pin Threshold
2
For more information
www.linear.com/LTC3638
LTC3638
ELECTRICAL CHARACTERISTICS
SYMBOL
V
FB(ADJ)
V
FBH
I
FB
V
FB(FIXED)
PARAMETER
Feedback Comparator Threshold
(Adjustable Output)
Feedback Comparator Hysteresis
(Adjustable Output)
Feedback Pin Current
Feedback Comparator Thresholds
(Fixed Output)
Output Supply (V
FB
)
V
FB
Rising, V
PRG1
= V
PRG2
= 0V
LTC3638E, LTC3638I
LTC3638H, LTC3638MP
V
FB
Falling, V
PRG1
= V
PRG2
= 0V
V
FB
= 1V, V
PRG1
= V
PRG2
= 0V
V
FB
Rising, V
PRG1
= SS, V
PRG2
= 0V
V
FB
Falling, V
PRG1
= SS, V
PRG2
= 0V
V
FB
Rising, V
PRG1
= 0V, V
PRG2
= SS
V
FB
Falling, V
PRG1
= 0V, V
PRG2
= SS
V
FB
Rising, V
PRG1
= V
PRG2
= SS
V
FB
Falling, V
PRG1
= V
PRG2
= SS
Operation
I
PEAK
R
ON
I
LSW
I
SS
t
INT(SS)
Peak Current Comparator Threshold
I
SET
Floating
100k Resistor from I
SET
to GND
I
SET
Shorted to GND
I
SW
= –100mA
V
IN
= 140V, SW = 0V
V
SS
< 2.5V
SS Pin Floating
4
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The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
0.792
0.788
3
–10
4.94
4.91
3.25
3.23
1.78
1.77
500
250
40
0.800
0.800
5
0
5.015
4.985
3.31
3.29
1.81
1.80
575
300
60
1.8
0.1
5
1
0.808
0.812
9
10
5.09
5.06
3.37
3.35
1.84
1.83
650
350
80
1
6
V
V
mV
nA
V
V
V
V
V
V
mA
mA
mA
Ω
μA
μA
ms
Power Switch On-Resistance
Switch Pin Leakage Current
Soft-Start Pin Pull-Up Current
Internal Soft-Start Time
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
T
J
≈ T
A
. 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 (T
J
, in °C) is calculated from the ambient
temperature (T
A
, in °C) and power dissipation (P
D
, in Watts) according to
the formula:
T
J
= T
A
+ (P
D
•
θ
JA
)
where
θ
JA
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.
3638fa
For more information
www.linear.com/LTC3638
3
LTC3638
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current,
V
OUT
= 5V
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
V
IN
= 12V
V
IN
= 48V
V
IN
= 140V
10
100
LOAD CURRENT (mA)
1000
3638 G01
Efficiency vs Load Current,
V
OUT
= 3.3V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
V
IN
= 12V
V
IN
= 48V
V
IN
= 140V
10
100
LOAD CURRENT (mA)
1000
3638 G02
Efficiency vs Load Current,
V
OUT
= 1.8V
100
90
80
70
60
50
40
30
20
10
0
0.1
1
V
IN
= 12V
V
IN
= 48V
V
IN
= 140V
10
100
LOAD CURRENT (mA)
1000
3638 G03
FIGURE 14 CIRCUIT
FIGURE 14 CIRCUIT
FIGURE 14 CIRCUIT
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
Efficiency vs Input Voltage,
V
OUT
= 5V
FIGURE 14 CIRCUIT
THRESHOLD VOLTAGE (mV)
Feedback Comparator Trip
Threshold vs Temperature
802
RUN OR OVLO THRESHOLD VOLTAGE (V)
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
1.08
RUN and OVLO Thresholds vs
Temperature
RISING
801
800
799
FALLING
I
LOAD
= 250mA
I
LOAD
= 10mA
I
LOAD
= 1mA
0
25
75
50
100
INPUT VOLTAGE (V)
125
150
3638 G04
798
–55
–25
95
5
35
65
TEMPERATURE (°C)
125
155
1.06
–55 –25
3638 G05
65
35
95
5
TEMPERATURE (°C)
125
155
3638 G06
Peak Current Trip Threshold
vs R
ISET
600
PEAK CURRENT TRIP THRESHOLD (mA)
500
PEAK CURRENT (mA)
400
300
200
100
0
700
600
500
400
300
200
100
0
25
50
75
100 125 150 175 200
R
ISET
(k )
3638 G07
Peak Current Trip Threshold
vs Temperature and I
SET
700
I
SET
OPEN
PEAK CURRENT (mA)
600
500
400
300
200
100
125
155
0
Peak Current Trip Threshold
vs Input Voltage
I
SET
OPEN
R
ISET
= 100k
R
ISET
= 100k
I
SET
= GND
–25
5
35
65
95
TEMPERATURE (°C)
I
SET
= GND
0
30
60
90
120
150
3638 G09
0
–55
3638 G08
V
IN
VOLTAGE (V)
4
3638fa
For more information
www.linear.com/LTC3638
LTC3638
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Supply Current
vs Input Voltage
15
SLEEP
V
IN
SUPPLY CURRENT (µA)
V
IN
SUPPLY CURRENT (µA)
10
35
30
25
20
15
10
5
120
150
3638 G10
3638 G11
Quiescent Supply Current
vs Temperature
V
IN
= 140V
SWITCH PIN CURRENT (µA)
15
10
5
0
–5
–10
SHUTDOWN
–25
65
35
5
95
TEMPERATURE (°C)
125
155
Switch Pin Current
vs Temperature
V
IN
= 140V
SLEEP MODE
SW = 0.8V
CURRENT INTO SW
SLEEP
5
SHUTDOWN
0
0
30
60
90
V
IN
VOLTAGE (V)
SW = 0V
CURRENT OUT OF SW
0
–55
–15
–55 –25
5
65
95
35
TEMPERATURE (°C)
125
155
3638 G12
Switch On-Resistance
vs Input Voltage
3.0
Switch On-Resistance
vs Temperature
4
I
SW
= 250mA
OUTPUT
VOLTAGE
50mV/DIV
LOAD
CURRENT
100mA/DIV
Load Step Transient Response
2.5
SWITCH ON-RESISTANCE ( )
SWITCH ON-RESISTANCE ( )
3
2.0
2
1.5
1
V
IN
= 48V
200µs/DIV
V
OUT
= 3.3V
1mA TO 250mA LOAD STEP
FIGURE 15 CIRCUIT
3638 G15
1.0
0
30
60
90
V
IN
VOLTAGE (V)
120
150
3638 G13
0
–55
–25
5
65
95
35
TEMPERATURE (°C)
125
155
3638 G14
Operating Waveforms, V
IN
= 48V
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
20V/DIV
INDUCTOR
CURRENT
500mA/DIV
Operating Waveforms, V
IN
= 140V
OUTPUT
VOLTAGE
50mV/DIV
SWITCH
VOLTAGE
50V/DIV
INDUCTOR
CURRENT
500mA/DIV
Short-Circuit and Recovery
OUTPUT
VOLTAGE
1V/DIV
INDUCTOR
CURRENT
500mA/DIV
V
IN
= 48V
10µs/DIV
V
OUT
= 3.3V
I
OUT
= 250mA
FIGURE 15 CIRCUIT
3638 G16
V
IN
= 140V
10µs/DIV
V
OUT
= 3.3V
I
OUT
= 250mA
FIGURE 15 CIRCUIT
3638 G17
500µs/DIV
FIGURE 15 CIRCUIT
3638 G18
3638fa
For more information
www.linear.com/LTC3638
5
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