LT3954_15 Datasheet, PDF (1/26 Pages) Linear Technology – 40VIN LED Converter with Internal PWM Generator

FEATURES
n _{3000:1 True Color PWM™ Dimming for LEDs}
n _{Wide VIN Range: 4.5V to 40V}
n _{Rail-to-Rail Current Sense Range: 0V to 40V}
n _{Internal 40V/5A Switch}
n _{Programmable PWM Dimming Signal Generator}
n _{Constant Current (±3%) and Constant-Voltage}
(±2%) Regulation
n _{Accurate Analog Dimming}
n _{Drives LEDs in Boost, SEPIC, CUK, Buck Mode,}
Buck-Boost Mode, or Flyback Configuration
n _{Output Short-Circuit Protected Boost}
n _{Open LED Protection and Reporting}
n _{Adjustable Switching Frequency: 100kHz to 1MHz}
n _{Programmable VIN UVLO with Hysteresis}
n _{C/10 Indication for Battery Chargers}
n _{Low Shutdown Current: <1µA}
n _{Thermally Enhanced 5mm × 6mm QFN Package}
APPLICATIONS
n _{High Power LEDs}
n _{Output Short-Circuit Protected Boost}
n _{Battery and SuperCap Chargers}
n _{Accurate Current Limited Voltage Regulators}
LT3954
40V_IN LED Converter with
Internal PWM Generator
DESCRIPTION
The LT^®3954 is a DC/DC converter designed to operate as
a constant-current source and constant-voltage regulator.
It features an internal low side N-channel MOSFET rated
for 40V/5A. The LT3954 is ideally suited for driving 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 LT3954 senses output current at the high side or at
the low side of the load. The internal PWM generator can
be configured to self-oscillate at fixed frequency with duty
ratio programmable 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
95% Efficiency 20W Boost LED Driver with Internal PWM Dimming
V_IN
5V TO 30V
DIM
4.7µF
124k
22µH
499k
4.7µF
V_IN
SW
×3
EN/UVLO
PGND
147k
V_REF
ISP
1M
LT3954
CTRL
INTV_CC
165k
ISN
0.38Ω
100k
VMODE
DIM/SS
1M
FB
37.4k
PWM
SYNC
RT
PWMOUT
10nF
28.7k
350kHz
V_C GND GNDK INTV_CC
5.1k
INTV_CC
47nF
300Hz ^4.7nF
1µF
650mA
PWM Dimming Waveforms at
Various DIM Voltage Settings
20W LED STRING
(CURRENT DERATED
FOR V_IN < 9V)
I_LED
0.65A/DIV
3954 TA01a
V_IN = 24V
V_LED = 32V
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%
3954 TA01b
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
3954fa
For more information www.linear.com/3954
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