LT3478/LT3478-1
4.5A Monolithic LED
Drivers with True Color
PWM Dimming
DESCRIPTIO
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FEATURES
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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:
100mA to 1050mA (LT3478-1)
(10mV to 105mV)/RSENSE (LT3478)
Program LED Current De-Rating vs Temperature
Separate Inductor Supply Input
Inrush Current Protection
Programmable Soft-Start
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
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APPLICATIO S
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High Power LED Driver
Automotive Lighting
The LT®3478/LT3478-1 are 4.5A step-up DC/DC converters designed to drive LEDs with a constant current over
a wide programmable range. Series connection of the
LEDs provides identical LED currents for uniform brightness without the need for ballast resistors and expensive
factory calibration.
The LT3478-1 reduces external component count and cost
by integrating the LED current sense resistor. The LT3478
uses an external sense resistor to extend the maximum
programmable LED current beyond 1A and also to achieve
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
high power LED driver applications such as automotive TFT
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.
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.
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TYPICAL APPLICATIO
Automotive TFT LCD Backlight
VIN 8V TO 16V
VIN
VS
L
10µF
SW
OUT
VREF
45.3k
CTRL2
LT3478-1
0.1Ω
RSENSE
(LT3478)
LED
OVPSET
54.9k
90
85
CTRL1
130k
ILED = 700mA
fOSC = 500kHz
PWM DUTY CYCLE = 100%
95
SHDN
EFFICIENCY (%)
4.7µF
Efficiency vs VIN
100
10µH
PWM
1µF
SS
700mA
15W
6 LEDs
(WHITE)
RT
VC
0.1µF
69.8k
PWM DIMMING
CONTROL
6 LEDs LUXEON III (WHITE)
80
8
10
12
VIN (V)
14
16
3478 TA01b
3478 TA01
34781f
1
