LT3954
1
3954fa
For more information www.linear.com/3954
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
40V
IN
LED Converter with
Internal PWM Generator
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 , LT C , LT M , 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.
95% Efficiency 20W Boost LED Driver with Internal PWM Dimming
PWM Dimming Waveforms at
Various DIM Voltage Settings
n
3000:1 True Color PWM™ Dimming for LEDs
n
Wide V
IN
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 V
IN
UVLO with Hysteresis
n
C/10 Indication for Battery Chargers
n
Low Shutdown Current: <1µA
n
Thermally Enhanced 5mm × 6mm QFN Package
n
High Power LEDs
n
Output Short-Circuit Protected Boost
n
Battery and SuperCap Chargers
n
Accurate Current Limited Voltage Regulators
V
IN
SW
LT3954
GNDK
GNDV
C
INTV
CC
EN/UVLO
PGND
V
REF
ISP
1M
100k
INTV
CC
499k
4.7µF
4.7µF
×3
4.7nF
V
IN
47nF
300Hz
147k
5.1k
28.7k
350kHz
1µF
165k
124k
CTRL
37.4k
1M
0.38Ω
650mA
INTV
CC
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
3954 TA01a
VMODE
DIM/SSDIM
PWM
RT
ISN
FB
SYNC
PWMOUT
20W LED STRING
FOR V
IN
< 9V)
10nF
0.5ms/DIV
V
DIM
= 8V
DC
PWM
V
DIM
= 3.87V
DC
PWM
= 50%
V
DIM
= 1.47V
DC
PWM
= 10%
V
DIM
= 0V
DC
PWM
= 2.8%
3954 TA01b
V
IN
= 24V
V
= 32V
I
LED
