LT3956
80V , 80V
IN
OUT
Constant-Current,
Constant-Voltage Converter
DescripTion
FeaTures
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3000:1 True Color PWMTM Dimming
The LT®3956 is a DC/DC converter designed to operate as
a constant-current source and constant-voltage regulator.
It is ideally suited for driving high current LEDs. It features
an internal low side N-channel power MOSFET rated for
84V at 3.3A and driven from an internal regulated 7.15V
supply. The fixed frequency, current-mode architecture
results in stable operation over a wide range of supply
and output voltages. A ground referenced voltage FB pin
serves as the input for several LED protection features,
and also makes it possible for the converter to operate
as a constant-voltage source. A frequency adjust pin
allows the user to program the frequency from 100kHz
to 1MHz to optimize efficiency, performance or external
component size.
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Wide Input Voltage Range: 4.5V to 80V
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Output Voltage Up to 80V
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Internal 3.3A/84V Switch
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Constant-Current and Constant-Voltage Regulation
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250mV High Side Current Sense
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Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
SEPIC or Flyback Topology
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Adjustable Frequency: 100kHz to 1MHz
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Open LED Protection
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Programmable Undervoltage Lockout with Hysteresis
Constant-Voltage Loop Status Pin
PWM Disconnect Switch Driver
CTRL Pin Adjusts High Side Current Sense Threshold
Low Shutdown Current: <1µA
Programmable Soft-Start
Available in the 36-Lead (5mm × 6mm) QFN Package
The LT3956 senses output current at the high side of the
LED string. High side current sensing is the most flexible
scheme for driving LEDs, allowing boost, buck mode or
buck-boost mode configuration. The PWM input provides
LED dimming ratios of up to 3000:1, and the CTRL input
provides additional analog dimming capability.
applicaTions
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High Power LED
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L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 7199560 and 7321203.
Battery Charger
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Accurate Current Limited Voltage Regulator
Typical applicaTion
Efficiency vs VIN
94% Efficient 25W White LED Headlamp Driver
V
, 6V TO 60V
IN
D1
22µH
(80V TRANSIENT)
100
2.2µF
s 2
2.2µF
s 5
332k
V
SW
IN
EN/UVLO
PGND
96
92
88
100k
V
ISP
REF
332k
LT3956
0.68Ω
370mA
CTRL
ISN
FB
INTV
CC
40.2k
1M
100k
VMODE
PWM
SS
25W LED STRING
16.2k
84
RT
PWMOUT
GND INTV
V
C
CC
80
0
20
60
80
40
(V)
28.7k
375kHz
34k
4.7nF
INTV
CC
V
IN
4.7µF
47nF
M1
3956 TA01b
3956 TA01a
3956f
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