SC4539_08 Datasheet, PDF (1/14 Pages) Semtech Corporation – High Effi ciency Boost Converter for up to 6 LEDS

SC4539
High Efficiency Boost Converter
for up to 6 LEDS
POWER MANAGEMENT
Features
„ Input voltage range — 2.8V to 5.5V
„ Programmable LED current up to 30mA
„ Current-mode PWM control — 800kHz
„ Soft-start to reduce in-rush current
„ PWM dimming — 100Hz to 50kHz
„ PWM dimming at ISET — Analog and filtered
„ Over-voltage protection — 22V (minimum)
„ Under-voltage lockout (UVLO)
„ Thermal shutdown
„ Shutdown current — <0.1μA (typical)
„ Ultra-thin package — 2mm x 2mm x 0.6mm
„ Lead-free package, WEEE and RoHS compliant
Applications
„ DSLR, DSC, and Video Cameras
„ Cellular handsets
„ Portable media players
„ Personal navigation systems
„ Satellite radio
„ Handheld video games
Typical Application Circuit
Description
The SC4539 is designed to regulate current for a series
string of white LEDs in LCD backlighting applications
where small size and high efficiency are priorities. This
device integrates an 800kHz current-mode PWM boost
converter and a 30mA programmable low dropout current
sink regulator.
An external resistor sets the LED current up to 30mA.
PWM dimming (100Hz to 50kHz) may be applied directly
to the enable (EN) pin, or dimming can be controlled by
applying an analog signal to the ISET circuit. The boost
circuit can output up to 22V (guaranteed) to drive up to 6
LEDs in series. The current regulator protects against
shorts between the BL and OUT pins and also eliminates
backlight glow during shutdown when using LEDs with
high leakage. Under-voltage lockout and thermal shut-
down provide additional protection. A small external
capacitor and series resistor control soft-start and loop
compensation. Over-voltage detection protects the
SC4539 if the BL pin is floating or shorted to ground.
The SC4539 is available in an MLPD-8 pin 2mm x 2mm x
0.6mm package, with a rated temperature range of -40°C
to +85°C.
2.8 to
5.5V
CIN
L1
IN
D
LX
OUT
SC4539
COUT
Enable and
EN
PWM dimming
RISET
ISET
CCOMP _RCOMP
COMP
BL
GND
June 20, 2008
© 2008 Semtech Corporation
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