LT3957 Datasheet PDF - Linear Technology

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LT3957
Linear Technology

Part Number LT3957
Description SEPIC and Inverting Converter
Page 28 Pages


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FEATURES
n Wide Input Voltage Range: 3V to 40V
n Single Feedback Pin for Positive or Negative
Output Voltage
n Internal 5A/40V Power Switch
n Current Mode Control Provides Excellent Transient
Response
n Programmable Operating Frequency (100kHz to
1MHz) with One External Resistor
n Synchronizable to an External Clock
n Low Shutdown Current < 1μA
n Internal 5.2V Low Dropout Voltage Regulator
n Programmable Input Undervoltage Lockout with
Hysteresis
n Programmable Soft-Start
n Thermally Enhanced QFN (5mm × 6mm) Package
APPLICATIONS
n Automotive
n Telecom
n Industrial
LT3957
Boost, Flyback, SEPIC and
Inverting Converter
with 5A, 40V Switch
DESCRIPTION
The LT®3957 is a wide input range, current mode DC/DC
converter which is capable of generating either positive
or negative output voltages. It can be configured as either
a boost, flyback, SEPIC or inverting converter. It features
an internal low side N-channel power MOSFET rated for
40V at 5A and driven from an internal regulated 5.2V
supply. The fixed frequency, current-mode architecture
results in stable operation over a wide range of supply
and output voltages.
The operating frequency of LT3957 can be set with an
external resistor over a 100kHz to 1MHz range, and can
be synchronized to an external clock using the SYNC pin.
A minimum operating supply voltage of 3V, and a low
shutdown quiescent current of less than 1μA, make the
LT3957 ideally suited for battery-powered systems.
The LT3957 features soft-start and frequency foldback
functions to limit inductor current during start-up.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
No RSENSE and ThinSOT are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents pending.
TYPICAL APPLICATION
VIN
4.5V TO 16V
High Efficiency Output Boost Converter
10μH
10μF
200k
VIN SW
EN/UVLO
GND
95.3k
LT3957
SGND
SENSE1
SYNC
SENSE2
FBX
RT SS
VC INTVCC
41.2k
300kHz
0.33μF 6.8k
4.7μF
22nF
10μF
s2
VOUT
24V
600mA
226k
15.8k
3957 TA01a
Efficiency vs Output Current
100
VIN = 12V
95
90
85
80
75
70
0
100 200 300 400 500 600
OUTPUT CURRENT (mA)
3957 TA01b
3957f
1
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LT3957
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN/UVLO (Note 5), SW ......................................40V
INTVCC ......................................................VIN + 0.3V, 8V
SYNC ..........................................................................8V
VC, SS.........................................................................3V
RT ............................................................................................... 1.5V
SENSE1, SGND .................. Internally Connected to GND
SENSE2..................................................................±0.3V
FBX ................................................................. –6V to 6V
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range .................. –65°C to 125°C
PIN CONFIGURATION
TOP VIEW
36 35 34 33 32 31 30
NC 1
NC 2
SENSE2 3
SGND 4
SGND
37
SENSE1 6
SW 8
SW 9
NC 10
SW
38
12 13 14 15 16 17
28 INTVCC
27 VIN
25 EN/UVLO
24 SGND
23 SGND
21 SW
20 SW
UHE PACKAGE
36-LEAD (5mm s 6mm) PLASTIC QFN
TJMAX = 125°C, θJA = 42°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 37) IS SGND, MUST BE SOLDERED TO SGND PLANE
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO SW PLANE
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3957EUHE#PBF
LT3957EUHE#TRPBF
3957
36-Lead (5mm × 6mm) Plastic QFN
–40°C to 125°C
LT3957IUHE#PBF
LT3957IUHE#TRPBF
3957
36-Lead (5mm × 6mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
2
3957f
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LT3957
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temp-
erature range, otherwise specifications are at TA ≈ TJ = 25°C. VIN = 24V, EN/UVLO = 24V, SENSE2 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
VIN Operating Range
3 40 V
VIN Shutdown IQ
EN/UVLO = 0V
EN/UVLO = 1.15V
0.1 1
6
μA
μA
VIN Operating IQ
VIN Operating IQ with Internal LDO Disabled
SW Pin Current Limit
VC = 0.3V, RT = 41.2k
VC = 0.3V, RT = 41.2k, INTVCC = 5.5V
l5
1.7 2.3
350 400
5.9 6.8
mA
μA
A
SW Pin On Voltage
SENSE2 Input Bias Current
ISW = 3A
Current Out of Pin
100 mV
–65 μA
Error Amplifier
FBX Regulation Voltage (VFBX(REG))
FBX > 0V (Note 3)
FBX < 0V (Note 3)
l 1.569 1.6 1.631
l –0.816 –0.800 –0.784
V
V
FBX Overvoltage Lockout
FBX > 0V (Note 4)
FBX < 0V (Note 4)
6 8 10
7 11 14
%
%
FBX Pin Input Current
FBX = 1.6V (Note 3)
FBX = –0.8V (Note 3)
70 100
–10 10
nA
nA
Transconductance gm (ΔIVC /ΔFBX)
VC Output Impedance
(Note 3)
(Note 3)
230 μS
5 MΩ
VFBX Line Regulation (ΔVFBX/[ΔVIN • VFBX(REG)])
VC Current Mode Gain (ΔVVC /ΔVSENSE)
VC Source Current
FBX > 0V, 3V < VIN < 40V (Notes 3, 6)
FBX < 0V, 3V < VIN < 40V (Notes 3, 6)
VC = 1.5V, FBX = 0V, Current Out of Pin
0.04 0.06
0.03 0.06
10
–15
%/ V
%/ V
V/ V
μA
VC Sink Current
FBX = 1.7V
FBX = –0.85V
12 μA
11 μA
Oscillator
Switching Frequency
RT Voltage
RT = 140k to SGND, FBX = 1.6V, VC = 1.5V
RT = 41.2k to SGND, FBX = 1.6V, VC = 1.5V
RT = 10.5k to SGND, FBX = 1.6V, VC = 1.5V
FBX = 1.6V
80 100 120
270 300 330
850 1000 1200
1.2
kHz
kHz
kHz
V
SW Minimum Off-Time
220 275
ns
SW Minimum On-Time
240 320
ns
SYNC Input Low
0.4
SYNC Input High
1.5
SS Pull-Up Current
SS = 0V, Current Out of Pin
–10 μA
Low Dropout Regulator
INTVCC Regulation Voltage
INTVCC Undervoltage Lockout Threshold
Falling INTVCC
UVLO Hysteresis
l5
2.6
5.2 5.45
2.7 2.85
0.15
V
V
V
3957f
3
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LT3957
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temp-
erature range, otherwise specifications are at TA ≈ TJ = 25°C. VIN = 24V, EN/UVLO = 24V, SENSE2 = 0V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
INTVCC Current Limit
INTVCC Load Regulation (ΔVINTVCC / VINTVCC)
INTVCC Line Regulation (ΔVINTVCC / [ΔVIN • VINTVCC])
Dropout Voltage (VIN – VINTVCC)
INTVCC Current in Shutdown
INTVCC Voltage to Bypass Internal LDO
Logic Inputs
VIN = 40V
VIN = 15V
0 < IINTVCC < 20mA, VIN = 8V
6V < VIN < 40V
VIN = 5V, IINTVCC = 20mA, VC = 0V
EN/UVLO = 0V, INTVCC = 6V
32 40 55
95
–1 –0.5
0.02 0.05
450
17
5.5
mA
mA
%
%/ V
mV
μA
V
EN/UVLO Threshold Voltage Falling
EN/UVLO Voltage Hysteresis
VIN = INTVCC = 6V
l 1.17 1.22 1.27
20
V
mV
EN/UVLO Input Low Voltage
EN/UVLO Pin Bias Current Low
IVIN Drops Below 1μA
EN/UVLO = 1.15V
0.4
1.7 2 2.5
V
μA
EN/UVLO Pin Bias Current High
EN/UVLO = 1.33V
20 100
nA
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 LT3957E is guaranteed to meet performance specifications
from the 0°C to 125°C operating junction temperature. Specifications over
the –40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LT3957I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3: The LT3957 is tested in a feedback loop which servos VFBX to the
reference voltages (1.6V and –0.8V) with the VC pin forced to 1.3V.
Note 4: FBX overvoltage lockout is measured at VFBX(OVERVOLTAGE) relative
to regulated VFBX(REG).
Note 5: For 3V ≤ VIN < 6V, the EN/UVLO pin must not exceed VIN.
Note 6: EN/UVLO = 1.33V when VIN = 3V.
TYPICAL PERFORMANCE CHARACTERISTICS TA ≈ TJ = 25°C, unless otherwise noted.
Positive Feedback Voltage
vs Temperature, VIN
1605
1600
VIN = 24V
VIN = 40V
1590
VIN = 8V
1585
VIN = INTVCC = 3V,
SHDN/UVLO = 1.33V
1580
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3957 G01
Negative Feedback Voltage
vs Temperature, VIN
–788
–790
–792
VIN = INTVCC = 3V
SHDN/UVLO = 1.33V
–794
–796
VIN = 8V
–798
–800
–802
VIN = 24V
VIN = 40V
–804
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3957 G02
4
Quiescent Current
vs Temperature, VIN
1.8
1.7 VIN = 40V
VIN = 24V
1.6
1.5 VIN = INTVCC = 3V
1.4
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3957 G03
3957f
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