LT3478/LT3478-1
4.5A Monolithic LED
Drivers with True Color
PWM Dimming
U
DESCRIPTIO
FEATURES
The LT®3478/LT3478-1 are 4.5A step-up DC/DC convert-
ers designed to drive LEDs with a constant current over
a wide programmable range. Series connection of the
LEDs provides identical LED currents for uniform bright-
ness without the need for ballast resistors and expensive
factory calibration.
■
True Color PWM™ Dimming Delivers Constant LED
Color with Up to 3000:1 Range
■
Wide Input Voltage Range: 2.8V to 36V
■
4.5A, 60mΩ, 42V Internal Switch
■
Drives LEDs in Boost, Buck-Boost or Buck Modes
■
Integrated Resistors for Inductor and LED Current
Sensing
Program LED Current:
TheLT3478-1reducesexternalcomponentcountandcost
by integrating the LED current sense resistor. The LT3478
uses an external sense resistor to extend the maximum
programmableLEDcurrentbeyond1Aandalsotoachieve
greater accuracy when programming low LED currents.
Operating frequency can be set with an external resistor
from 200kHz up to 2.25MHz. Unique circuitry allows a
PWM dimming range up to 3000:1 while maintaining
constant LED color. The LT3478/LT3478-1 are ideal for
highpowerLEDdriverapplicationssuchasautomotiveTFT
LCD backlights, courtesy lighting and heads-up displays.
One of two CTRL pins can be used to program maximum
LED current. The other CTRL pin can be used to program
a reduction in maximum LED current vs temperature to
maximize LED usage and improve reliability.
■
100mA to 1050mA (LT3478-1)
(10mV to 105mV)/R
Program LED Current De-Rating vs Temperature
Separate Inductor Supply Input
Inrush Current Protection
Programmable Soft-Start
(LT3478)
SENSE
■
■
■
■
■
■
■
Fixed Frequency Operation from 200kHz to 2.25MHz
Open LED Protection (Programmable OVP)
Accurate Shutdown/UVLO Threshold with
Programmable Hysteresis
■
16-Pin Thermally Enhanced TSSOP Package
U
APPLICATIO S
■
High Power LED Driver
Automotive Lighting
Additional features include inrush current protection,
programmable open LED protection and programmable
soft-start. Each part is available in a 16-pin thermally
enhanced TSSOP Package.
■
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents Pending.
U
TYPICAL APPLICATIO
Automotive TFT LCD Backlight
Efficiency vs V
IN
100
95
90
85
80
10µH
V
IN
8V TO 16V
I
f
= 700mA
= 500kHz
PWM DUTY CYCLE = 100%
LED
OSC
10µF
4.7µF
V
IN
V
S
L
SW
SHDN
OUT
V
REF
0.1Ω
SENSE
(LT3478)
R
45.3k
CTRL2
LT3478-1
LED
OVPSET
54.9k
130k
CTRL1
PWM
700mA
15W
SS
V
R
T
C
6 LEDs LUXEON III (WHITE)
12 14 16
(V)
6 LEDs
(WHITE)
8
10
1µF
0.1µF
69.8k
V
IN
3478 TA01b
PWM DIMMING
CONTROL
3478 TA01
34781f
1