LT1936
1.4A, 500kHz Step-Down
Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1936 is a current mode PWM step-down DC/DC
converter with an internal 1.9A power switch, packaged
in a tiny, thermally enhanced 8-lead MSOP The wide in-
.
put range of 3.6V to 36V makes the LT1936 suitable for
regulating power from a wide variety of sources, including
automotive batteries, 24V industrial supplies and unregu-
lated wall adapters. Its high operating frequency allows the
use of small, low cost inductors and ceramic capacitors,
resulting in low, predictable output ripple.
Cycle-by-cycle current limit, frequency foldback and
thermal shutdown provide protection against shorted
outputs, and soft-start eliminates input current surge
during start-up. Transient response can be optimized by
using external compensation components, or board space
can be minimized by using internal compensation. The
low current (<2μA) shutdown mode enables easy power
management in battery-powered systems.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Wide Input Range: 3.6V to 36V
Short-Circuit Protected Over Full Input Range
1.9A Guaranteed Minimum Switch Current
5V at 1.4A from 10V to 36V Input
3.3V at 1.4A from 7V to 36V Input
5V at 1.2A from 6.3V to 36V Input
3.3V at 1.2A from 4.5V to 36V Input
Output Adjustable Down to 1.20V
500kHz Fixed Frequency Operation
Soft-Start
Uses Small Ceramic Capacitors
Internal or External Compensation
Low Shutdown Current: <2μA
Thermally Enhanced 8-Lead MSOP Package
APPLICATIONS
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Automotive Battery Regulation
Industrial Control Supplies
Unregulated Wall Adapters
TYPICAL APPLICATION
3.3V Step-Down Converter
95
V
IN
4.5V TO 36V
V
IN
ON OFF
4.7μF
SHDN
LT1936
17.4k
COMP
V
C
FB
GND
10k
22μF
BOOST
SW
0.22μF
10μH
EFFICIENCY (%)
V
OUT
3.3V
1.2A
90
85
V
OUT
= 3.3V
80
75
70
1936 TA01a
Efficiency
V
IN
= 12V
V
OUT
= 5V
65
0
0.5
1
LOAD CURRENT (A)
1.5
1936 TA01b
1936fd
1
LT1936
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
BOOST
V
IN
SW
GND
1
2
3
4
8
7
6
5
COMP
V
C
FB
SHDN
V
IN
Voltage ................................................. –0.4V to 36V
BOOST Voltage .........................................................43V
BOOST Above SW Voltage ........................................20V
SHDN
Voltage ............................................ –0.4V to 36V
FB, V
C
, COMP Voltage .................................................6V
Operating Temperature Range (Note 2)
LT1936E ............................................... –40°C to 85°C
LT1936I .............................................. –40°C to 125°C
LT1936H ............................................ –40°C to 150°C
Maximum Junction Temperature
LT1936E, LT1936I ............................................. 125°C
LT1936H ........................................................... 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
9
MS8E PACKAGE
8-LEAD PLASTIC MSOP
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT1936EMS8E#PBF
LT1936IMS8E#PBF
LT1936HMS8E#PBF
LEAD BASED FINISH
LT1936EMS8E
LT1936IMS8E
LT1936HMS8E
TAPE AND REEL
LT1936EMS8E#TRPBF
LT1936IMS8E#TRPBF
LT1936HMS8E#TRPBF
TAPE AND REEL
LT1936EMS8E#TR
LT1936IMS8E#TR
LT1936HMS8E#TR
PART MARKING
LTBMT
LTBRV
LTBWB
PART MARKING
LTBMT
LTBRV
LTBWB
PACKAGE DESCRIPTION
8-Lead Plastic MSOP
8-Lead Plastic MSOP
8-Lead Plastic MSOP
PACKAGE DESCRIPTION
8-Lead Plastic MSOP
8-Lead Plastic MSOP
8-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
ELECTRICAL CHARACTERISTICS
PARAMETER
Undervoltage Lockout
Quiescent Current
Quiescent Current in Shutdown
FB Voltage
FB Pin Bias Current (Note 4)
FB Voltage Line Regulation
Error Amp gm
Error Amp Voltage Gain
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
BOOST
= 17V, unless otherwise noted. (Note 2)
CONDITIONS
V
FB
= 1.5V
V
SHDN
= 0V
●
MIN
TYP
3.45
1.8
0.1
MAX
3.6
2.5
2
1.215
200
300
UNITS
V
mA
μA
V
nA
nA
%/V
μS
1.175
1.200
50
50
0.01
250
150
V
FB
= 1.20V, E and I Grades
H Grade
V
IN
= 5V to 36V
V
C
= 0.5V, I
VC
= ±5μA
V
C
= 0.8V, 1.2V
●
●
1936fd
2
LT1936
ELECTRICAL CHARACTERISTICS
V
C
Clamp
V
C
Switch Threshold
Internal Compensation R
Internal Compensation C
COMP Pin Leakage
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Minimum BOOST Voltage Above SW
BOOST Pin Current
BOOST Pin Leakage
SHDN
Input Voltage High
SHDN
Input Voltage Low
SHDN
Pin Current
V
SHDN
= 2.3V (Note 5)
V
SHDN
= 12V (Note 5)
V
SHDN
= 0V
34
140
0.01
I
SW
= 1.2A
I
SW
= 1.2A
V
SW
= 0V
2.3
0.3
50
240
0.1
2
28
0.1
(Note 3)
I
SW
= 1.2A
V
COMP
= 1V
V
COMP
= 1.8V, E and I Grades
H Grade
V
FB
= 1.1V
V
FB
= 0V
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, V
BOOST
= 17V, unless otherwise noted. (Note 2)
1.8
0.7
50
150
1
2
400
87
1.9
500
40
92
2.2
410
2.6
520
2
2.2
50
1
600
V
V
kΩ
pF
μA
μA
kHz
kHz
%
A
mV
μA
V
mA
μA
V
V
μA
μA
μA
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 LT1936E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT1936I specifications are
guaranteed over the –40°C to 125°C temperature range. The LT1936H
specifications are guaranteed over the –40°C to 150°C temperature range.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
Note 4:
Current flows out of pin.
Note 5:
Current flows into pin.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency, V
OUT
= 5V
100
100
Efficiency, V
OUT
= 3.3V
3.0
2.5
Switch Current Limit
90
EFFICIENCY (%)
V
IN
= 12V
V
IN
= 24V
EFFICIENCY (%)
90
V
IN
= 5V
CURRENT LIMIT (A)
2.0
1.5
1.0
0.5
0
0
0.5
1.0
LOAD CURRENT (A)
1.5
1936 G02
TYP
MIN
V
IN
= 12V
80
V
IN
= 24V
80
70
V
OUT
= 5V
T
A
= 25°C
D1 = DFLS140L
L1 = 15μH, TOKO D63CB
0
0.5
1.0
LOAD CURRENT (A)
1.5
1936 G01
70
V
OUT
= 3.3V
T
A
= 25°C
D1 = DFLS140L
L1 = 10μH, TOKO D63CB
60
60
0
20
40
60
DUTY CYCLE (%)
80
100
1936 G03
1936fd
3
LT1936
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Load Current
1.8
V
OUT
= 5V
1.8
Maximum Load Current
V
OUT
= 3.3V
SWITCH VOLTAGE DROP (mV)
600
500
400
300
200
100
0
Switch Voltage Drop
1.6
LOAD CURRENT (A)
L = 15μH
1.4
L = 10μH
LOAD CURRENT (A)
1.6
L = 10μH
T
A
= 85°C
T
A
= 25°C
T
A
= –45°C
1.4
L = 6.8μH
1.2
1.2
1.0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1936 G04
1.0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1936 G05
0
0.5
1.0
SWITCH CURRENT (A)
1.5
1936 G06
Feedback Voltage
1.210
3.8
Undervoltage Lockout
600
SWITCHING FREQUENCY (kHz)
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G08
Switching Frequency
1.205
FEEDBACK VOLTAGE (V)
3.6
UVLO (V)
550
1.200
3.4
500
1.195
3.2
1.190
450
1.185
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G07
3.0
–50 –25
0
400
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G09
Frequency Foldback
700
600
SWITCH CURRENT LIMIT (A)
500
400
300
200
100
0
0
0.5
1.0
FB PIN VOLTAGE (V)
1.5
1936 G10
Soft-Start
3.0
2.5
SHDN
PIN CURRENT (μA)
150
2.0
1.5
1.0
0.5
0
0
1
2
3
SHDN
PIN VOLTAGE (V)
4
1936 G11
SHDN
Pin Current
200
T
A
= 25°C
T
A
= 25°C
T
A
= 25°C
DC = 30%
SWITCHING FREQUENCY (kHz)
100
50
0
0
12
4
8
SHDN
PIN VOLTAGE (V)
16
1936 G12
1936fd
4
LT1936
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Input Voltage
7.0
6.5
INPUT VOLTAGE (V)
6.0
5.5
5.0
4.5
4.0
1
10
100
LOAD CURRENT (mA)
1000
1936 G13
Minimum Input Voltage
5.0
V
OUT
= 3.3V
T
A
= 25°C
L = 10μH
3.0
2.5
2.0
1.5
1.0
0.5
3.0
1
10
100
LOAD CURRENT (mA)
1000
1936 G14
Switch Current Limit
4.5
INPUT VOLTAGE (V)
4.0
3.5
SWITCH CURRENT LIMIT (A)
V
OUT
= 5V
T
A
= 25°C
L = 15μH
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G15
Switching Waveforms
V
SW
10V/DIV
I
L
500mA/DIV
V
OUT
20mV/DIV
V
IN
= 12V
V
OUT
= 3.3V
I
OUT
= 1A
L = 10μH
C
OUT
= 22μF
1μs/DIV
1936 G16
Switching Waveforms,
Discontinuous Mode
V
SW
10V/DIV
I
L
500mA/DIV
V
OUT
20mV/DIV
V
IN
= 12V
V
OUT
= 3.3V
I
OUT
= 50mA
L = 10μH
C
OUT
= 22μF
1μs/DIV
1936 G17
V
C
Voltages
2.5
60
40
CURRENT LIMIT CLAMP
1.5
V
C
PIN CURRENT (μA)
20
0
–20
–40
–60
Error Amp Output Current
T
A
= 25°C
V
C
= 0.5V
2.0
VC VOLTAGE (V)
1.0
SWITCHING THRESHOLD
0.5
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G18
0
1
FB PIN VOLTAGE (V)
2
1936 G19
1936fd
5
嵌入式系统
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