LT3955_15 Datasheet, PDF (1/30 Pages) Linear Technology – 60VIN LED Converter with Internal PWM Generator

Features
nn _{3000:1 True Color PWM™ Dimming for LEDs}
nn _{Wide VIN Range: 4.5V to 60V}
nn _{Rail-to-Rail Current Sense Range: 0V to 80V}
nn _{Internal 80V/3.5A Switch}
nn _{Programmable PWM Dimming Signal Generator}
nn _{Constant Current (±3%) and Constant-Voltage}
(±2%) Regulation
nn _{Accurate Analog Dimming}
nn _{Drives LEDs in Boost, SEPIC, CUK, Buck Mode,}
Buck-Boost Mode, or Flyback Configuration
nn _{Output Short-Circuit Protected Boost}
nn _{Open LED Protection and Reporting}
nn _{Adjustable Switching Frequency: 100kHz to 1MHz}
nn _{Programmable VIN UVLO with Hysteresis}
nn _{C/10 Indication for Battery Chargers}
nn _{Low Shutdown Current: <1µA}
nn _{Thermally Enhanced 5mm × 6mm QFN Package}
Applications
nn _{High Power LEDs}
nn _{Output Short-Circuit Protected Boost}
nn _{Battery and SuperCap Chargers}
nn _{Accurate Current Limited Voltage Regulators}
LT3955
60V_IN LED Converter with
Internal PWM Generator
Description
The LT^®3955 is a DC/DC converter designed to operate as
a constant-current source and constant-voltage regula-
tor. It features an internal low side N-channel MOSFET
rated for 80V/3.5A. The LT3955 is ideally suited for driv-
ing high current LEDs, but also has features to make it
suitable for charging batteries and supercapacitors. The
fixed frequency, current mode architecture results in
stable operation over a wide range of supply and output
voltages. A voltage feedback 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 LT3955 senses output current at the high side or at
the low side of the load. The PWM input can be configured
to self-oscillate at fixed frequency with duty ratio pro-
grammable from 4% to 96%. When driven by an external
signal, the PWM input provides LED dimming ratios of
up to 3000:1. 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, 7321203.
Typical Application
94% Efficiency 20W Boost LED Driver with Internal PWM Dimming
V_IN
5V TO 60V
DIM
4.7µF
×2
124k
22µH
499k
V_IN
EN/UVLO
SW
PGND
2.2µF
×5
147k
V_REF
ISP
1M
LT3955
CTRL
INTV_CC
165k
ISN
100k
VMODE
DIM/SS
PWM
RT
FB
SYNC
PWMOUT
0.82Ω
1M
16.9k
10nF
28.7k
V_C GND GNDK INTV_CC
350kHz
5.1k
INTV_CC
47nF
300Hz ^4.7nF
1µF
300mA
PWM Dimming Waveforms at
Various DIM Voltage Settings
I_LED
0.3A/DIV
20W LED STRING
(CURRENT DERATED
FOR V_IN < 9V)
V_IN = 24V
V_LED = 65V
0.5ms/DIV
V_DIM = 8V
DC_PWM = 97.2%
V_DIM = 3.87V
DC_PWM = 50%
V_DIM = 1.47V
DC_PWM = 10%
V_DIM = 0V
DC_PWM = 2.8%
3955 TA01b
3955 TA01a
NOTE: GND, GNDK AND SIGNAL LEVEL COMPONENTS MUST BE CONNECTED EXTERNALLY AS SHOWN.
AN INTERNAL CONNECTION BETWEEN GNDK AND PGND PINS PROVIDES GROUNDING TO THE SUPPLY.
3955fb
For more information www.linear.com/LT3955
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