
LT3956
FEATURES
80V IN , 80V OUT
Constant-Current,
Constant-Voltage Converter
DESCRIPTION
3000:1 True Color PWM TM Dimming
High Power LED
Battery Charger
Accurate Current Limited Voltage Regulator
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n Wide Input Voltage Range: 4.5V to 80V
n Output Voltage Up to 80V
n Internal 3.3A/84V Switch
n Constant-Current and Constant-Voltage Regulation
n 250mV High Side Current Sense
n Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
SEPIC or Flyback Topology
n Adjustable Frequency: 100kHz to 1MHz
n Open LED Protection
n Programmable Undervoltage Lockout with Hysteresis
n Constant-Voltage Loop Status Pin
n PWM Disconnect Switch Driver
n CTRL Pin Adjusts High Side Current Sense Threshold
n Low Shutdown Current: <1μA
n Programmable Soft-Start
n Available in the 36-Lead (5mm × 6mm) QFN Package
APPLICATIONS
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n
n
TYPICAL APPLICATION
94% Efficient 25W White LED Headlamp Driver
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.
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.
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.
Efficiency vs V IN
V IN , 6V TO 60V
(80V TRANSIENT)
22μH
D1
100
2.2μF
2
332k
V IN
EN/UVLO
SW
PGND
2.2μF
5
96
100k
INTV CC
100k
332k
40.2k
V REF
CTRL
VMODE
PWM
SS
LT3956
ISP
ISN
FB
0.68
1M
16.2k
370mA
25W LED STRING
92
88
84
47nF
28.7k
375kHz
RT
V C
34k
4.7nF
PWMOUT
GND INTV CC
INTV CC
4.7μF
M1
80
0
20
40
V IN (V)
60
80
3956 TA01b
3956 TA01a
3956f