LT3478 Datasheet, PDF (1/24 Pages) Linear Technology – 4.5A Monolithic LED Drivers with True Color PWM Dimming

FEATURES
■ _{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)/R_SENSE (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}
U
APPLICATIO S
■ _{High Power LED Driver}
■ _{Automotive Lighting}
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patents Pending.
LT3478/LT3478-1
4.5A Monolithic LED
Drivers with True Color
PWM Dimming
DESCRIPTIO
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.
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.
TYPICAL APPLICATIO
Automotive TFT LCD Backlight
V_IN 8V TO 16V
10µH
4.7µF
45.3k
54.9k
V_IN V_S L
SW
SHDN
OUT
V_REF
CTRL2 _LT3478-1
LED
OVPSET
10µF
0.1Ω
R_SENSE
(LT3478)
CTRL1
130k
PWM SS
1µF
PWM DIMMING
CONTROL
V_C
R_T
0.1µF 69.8k
700mA
15W
6 LEDs
(WHITE)
3478 TA01
Efficiency vs V_IN
100 _{ILED = 700mA}
f_OSC = 500kHz
PWM DUTY CYCLE = 100%
95
90
85
80
8
6 LEDs LUXEON III (WHITE)
10
12
V_IN (V)
14
16
3478 TA01b
34781f
1