LT3956_15 Datasheet, PDF (1/20 Pages) Linear Technology – Constant-Current, Constant-Voltage Converter

LT3956
Features
80V_IN, 80V_OUT
Constant-Current,
Constant-Voltage Converter
Description
n _{3000:1 True Color PWM}^TM _Dimming
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
n _{High Power LED}
n _{Battery Charger}
n _{Accurate Current Limited Voltage Regulator}
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.
Typical Application
V_IN, 6V TO 60V
(80V TRANSIENT)
2.2µF
s2
332k
100k
INTV_CC
100k
47nF
94% Efficient 25W White LED Headlamp Driver
22µH
D1
V_IN
EN/UVLO
SW
PGND
2.2µF
s5
V_REF
ISP
332k
LT3956
CTRL
40.2k
ISN
0.68Ω
1M
VMODE
PWM
SS
RT
V_C
FB
PWMOUT
GND INTV_CC
16.2k
28.7k
375kHz
34k
4.7nF
INTV_CC
4.7µF
370mA
25W LED STRING
M1
3956 TA01a
100
96
92
88
84
80
0
Efficiency vs V_IN
20
40
60
80
V_IN (V)
3956 TA01b
3956f