LT1936
1.4A, 500kHz Step-Down
Switching Regulator
FEATURES
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DESCRIPTIO
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
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 input
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 capaci-
tors, resulting in low, predictable output ripple.
Cycle-by-cycle current limit, frequency foldback and ther-
mal 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 mini-
mized by using internal compensation. The low current
(<2µA) shutdown mode enables easy power management
in battery-powered systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Automotive Battery Regulation
Industrial Control Supplies
Unregulated Wall Adapters
TYPICAL APPLICATIO
V
IN
4.5V TO 36V
V
IN
ON OFF
4.7µF
SHDN
LT1936
3.3V Step-Down Converter
95
0.22µF
10µH
V
IN
= 12V
V
OUT
= 5V
BOOST
SW
90
85
EFFICIENCY (%)
17.4k
COMP
V
C
FB
GND
10k
V
OUT
3.3V
1.2A
80
75
70
22µF
1936 TA01a
65
0
U
Efficiency
V
OUT
= 3.3V
0.5
1
LOAD CURRENT (A)
1.5
1936 TA01b
U
U
1936fa
1
LT1936
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
BOOST
V
IN
SW
GND
1
2
3
4
8
7
6
5
COMP
V
C
FB
SHDN
9
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
LT1936EMS8E
LT1936IMS8E
LT1936HMS8E
MS8E PART MARKING
LTBMT
LTBRV
LTBWB
MS8E PACKAGE
8-LEAD PLASTIC MSOP
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 9) IS GND
MUST BE CONNECTED TO PCB
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes 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)
PARAMETER
Undervoltage Lockout
Quiescent Current
Quiescent Current in Shutdown
FB Voltage
FB Pin Bias Current (Note 4)
FB Voltage Line Regulation
Error Amp g
m
Error Amp Voltage Gain
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
I
SW
= 1.2A
2
I
SW
= 1.2A
V
COMP
= 1V
V
COMP
= 1.8V, E and I Grades
H Grade
V
FB
= 1.1V
V
FB
= 0V
●
●
●
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
V
V
kΩ
pF
1.175
1.200
50
50
0.01
250
150
1.8
0.7
50
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
●
●
1
2
400
87
1.9
500
40
92
2.2
410
2.6
520
2
2.2
600
2
U
µA
µA
kHz
kHz
%
A
mV
µA
V
1936fa
W
U
U
W W
W
LT1936
ELECTRICAL CHARACTERISTICS
The
●
denotes 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)
PARAMETER
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
V
SHDN
= 0V
34
140
0.01
CONDITIONS
I
SW
= 1.2A
V
SW
= 0V
2.3
0.3
50
240
0.1
MIN
TYP
28
0.1
MAX
50
1
UNITS
mA
µA
V
V
µA
µA
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
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.
High junction temperatures degrade operating lifetimes. Operating lifetime
at junction temperatures greater than 125°C is derated to 1000 hours.
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 PERFOR A CE CHARACTERISTICS
Efficiency, V
OUT
= 5V
100
100
CURRENT LIMIT (A)
90
V
IN
= 12V
V
IN
= 24V
EFFICIENCY (%)
EFFICIENCY (%)
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
60
U W
Efficiency, V
OUT
= 3.3V
3.0
2.5
90
V
IN
= 5V
2.0
1.5
1.0
0.5
0
0
0.5
1.0
LOAD CURRENT (A)
1.5
1936 G02
Switch Current Limit
TYP
MIN
V
IN
= 12V
80
V
IN
= 24V
70
V
OUT
= 3.3V
T
A
= 25°C
D1 = DFLS140L
L1 = 10µH, TOKO D63CB
60
0
20
60
40
DUTY CYCLE (%)
80
100
1936 G03
1936fa
3
LT1936
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Load Current
1.8
V
OUT
= 5V
1.8
SWITCH VOLTAGE DROP (mV)
1.6
LOAD CURRENT (A)
LOAD CURRENT (A)
L = 15µH
1.4
L = 10µH
1.2
1.0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1936 G04
Feedback Voltage
1.210
3.8
1.205
FEEDBACK VOLTAGE (V)
3.6
UVLO (V)
SWITCHING FREQUENCY (kHz)
1.200
1.195
1.190
1.185
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G07
Frequency Foldback
700
600
SWITCH CURRENT LIMIT (A)
T
A
= 25°C
SWITCHING FREQUENCY (kHz)
SHDN PIN CURRENT (µA)
500
400
300
200
100
0
0
1.0
0.5
FB PIN VOLTAGE (V)
1.5
1936 G10
4
U W
Maximum Load Current
600
V
OUT
= 3.3V
500
400
300
200
100
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1936 G05
Switch Voltage Drop
1.6
L = 10µH
T
A
= 85°C
T
A
= 25°C
T
A
= –45°C
1.4
L = 6.8µH
1.2
1.0
0
0.5
1.0
SWITCH CURRENT (A)
1.5
1936 G06
Undervoltage Lockout
600
Switching Frequency
550
3.4
500
3.2
450
3.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G08
400
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G09
Soft-Start
3.0
2.5
150
SHDN Pin Current
200
T
A
= 25°C
T
A
= 25°C
DC = 30%
2.0
1.5
1.0
0.5
0
0
1
2
3
SHDN PIN VOLTAGE (V)
4
1936 G11
100
50
0
0
12
4
8
SHDN PIN VOLTAGE (V)
16
1936 G12
1936fa
LT1936
TYPICAL PERFOR A CE CHARACTERISTICS
Minimum Input Voltage
8
V
OUT
= 5V
T
A
= 25°C
L = 15µH
TO START
INPUT VOLTAGE (V)
7
INPUT VOLTAGE (V)
TO START
5.0
4.5
4.0
3.5
TO RUN
SWITCH CURRENT LIMIT (A)
6
TO RUN
5
4
1
100
10
LOAD CURRENT (mA)
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
V
C
Voltages
2.5
2.0
VC VOLTAGE (V)
CURRENT LIMIT CLAMP
1.5
V
C
PIN CURRENT (µA)
1.0
SWITCHING THRESHOLD
0.5
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G18
U W
1000
1936 G13
Minimum Input Voltage
6.0
5.5
V
OUT
= 3.3V
T
A
= 25°C
L = 10µH
3.0
2.5
2.0
1.5
1.0
0.5
Switch Current Limit
3.0
0
10
100
LOAD CURRENT (mA)
1000
1936 G14
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1936 G15
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
Error Amp Output Current
60
40
20
0
–20
–40
–60
T
A
= 25°C
V
C
= 0.5V
0
1
FB PIN VOLTAGE (V)
2
1936 G19
1936fa
5
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