LT3755/LT3755-1/LT3755-2
40VIN, 75VOUT LED Controllers
Features
Description
3000:1 True Color PWM™ Dimming
Wide Input Voltage Range: 4.5V to 40V
Output Voltage Up to 75V
Constant-Current and Constant-Voltage Regulation
100mV High Side Current Sense
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 Improved Open LED Status Pin (LT3755-2)
n Frequency Synchronization (LT3755-1)
n PWM Disconnect Switch Driver
n CTRL Pin Provides Analog Dimming
n Low Shutdown Current: <1µA
n Programmable Soft-Start
n Thermally Enhanced 16-Lead QFN (3mm × 3mm)
and MSOP Packages
The LT®3755, LT3755-1 and LT3755-2 are DC/DC controllers designed to operate as a constant-current source for
driving high current LEDs. They drive a low side external
N-channel power MOSFET 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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The LT3755/LT3755-1/LT3755-2 sense 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
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. 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, 7321203.
High Power LED
n Battery Chargers
n Accurate Current Limited Voltage Regulators
n
Typical Application
50W White Automotive LED Headlamp Driver
Efficiency vs VIN
22µH
4.7µF
1M
185k
VIN
SHDN/UVLO
VREF
332k
40.2k
23.7k
0.1Ω
1A
ISN
GATE
100k
0.01µF
96
FB
ISP
LT3755-2
CTRL
INTVCC
100
4.7µF
1M
EFFICIENCY (%)
VIN
8V TO
40V
SENSE
28.7k
375kHz
OPENLED
PWM
SS
PWMOUT
RT
VC
GND INTVCC
10k
0.015Ω
50W
LED
STRING
92
88
84
80
4.7µF
0.001µF
0
10
20
VIN (V)
30
40
37551 TA01b
37551 TA01a
37551fd
