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LT3954_15

Description
40VIN LED Converter with Internal PWM Generator
File Size320KB,26 Pages
ManufacturerLinear ( ADI )
Websitehttp://www.analog.com/cn/index.html
Download Datasheet View All

LT3954_15 Overview

40VIN LED Converter with Internal PWM Generator

LT3954
40V
IN
LED Converter with
Internal PWM Generator
FEATURES
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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.
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3000:1 True Color PWM™ Dimming for LEDs
Wide V
IN
Range: 4.5V to 40V
Rail-to-Rail Current Sense Range: 0V to 40V
Internal 40V/5A Switch
Programmable PWM Dimming Signal Generator
Constant Current (±3%) and Constant-Voltage
(±2%) Regulation
Accurate Analog Dimming
Drives LEDs in Boost, SEPIC, CUK, Buck Mode,
Buck-Boost Mode, or Flyback Configuration
Output Short-Circuit Protected Boost
Open LED Protection and Reporting
Adjustable Switching Frequency: 100kHz to 1MHz
Programmable V
IN
UVLO with Hysteresis
C/10 Indication for Battery Chargers
Low Shutdown Current: <1µA
Thermally Enhanced 5mm × 6mm QFN Package
APPLICATIONS
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High Power LEDs
Output Short-Circuit Protected Boost
Battery and SuperCap Chargers
Accurate Current Limited Voltage Regulators
TYPICAL APPLICATION
95% Efficiency 20W Boost LED Driver with Internal PWM Dimming
V
IN
5V TO 30V
22µH
4.7µF
499k
147k
1M
165k
INTV
CC
100k
DIM
124k
V
IN
EN/UVLO
V
REF
LT3954
CTRL
ISN
1M
FB
VMODE
37.4k
DIM/SS
SYNC
PWM
RT
PWMOUT
V
C
GND GNDK INTV
CC
INTV
CC
1µF
20W LED STRING
(CURRENT DERATED
FOR V
IN
< 9V)
I
LED
0.65A/DIV
SW
PGND
ISP
0.38
650mA
4.7µF
×3
PWM Dimming Waveforms at
Various DIM Voltage Settings
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%
10nF
28.7k
350kHz
V
IN
= 24V
V
LED
= 32V
3954 TA01a
0.5ms/DIV
3954 TA01b
5.1k
47nF
300Hz 4.7nF
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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