LT3956
3956f
Typical applicaTion
FeaTures
applicaTions
DescripTion
80V
IN
, 80V
OUT
Constant-Current,
Constant-Voltage Converter
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.
94% Efficient 25W White LED Headlamp Driver
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
n
High Power LED
n
Battery Charger
n
Accurate Current Limited Voltage Regulator
V
IN
SW
LT3956
22µH
D1
GND
V
C
INTV
CC
EN/UVLO
PGND
V
REF
ISP
332k
100k
INTV
CC
332k
2.2µF
s
2
2.2µF
s
5
4.7nF
V
IN
, 6V TO 60V
(80V TRANSIENT)
47nF
100k
34k
28.7k
375kHz
4.7µF
40.2k
CTRL
16.2k
1M
0.68Ω
370mA
M1
INTV
CC
25W LED STRING
3956 TA01a
VMODE
PWM
SS
RT
ISN
FB
PWMOUT
Efficiency vs V
IN
V
IN
(V)
0
20
80
EFFICIENCY (%)
84
88
92
96
100
40
60
80
3956 TA01b
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.