SC4538 Datasheet, PDF (1/14 Pages) Semtech Corporation – High Effi ciency Boost Converter for up to 10 LEDs

SC4538
High Efficiency Boost Converter
POWER MANAGEMENT
for up to 10 LEDs
Features
Description
„ Input voltage range — 2.8V to 5.5V
„ Current-mode PWM control — 800kHz
„ Programmable LED current up to 30mA
„ Soft-start to reduce in-rush current
„ PWM dimming — 100Hz to 50kHz
„ Analog and filtered-PWM dimming at ISET
„ Over-voltage protection — 38V (min.)
„ Under-voltage lockout (UVLO)
„ Thermal shutdown
„ Shutdown current — <1μA
„ Ultra-thin package — 2mm x 2mm x 0.6mm
„ Lead-free package, WEEE and RoHS compliant
Applications
„ White LED Display Backlight Driver
„ Smartphones and PDAs
„ Cellular Handsets
„ MP3 and Portable Media Players
„ DSC, GPS, Satellite Radio, Game Players
The SC4538 is designed to regulate current for a series
chain 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 SC4538
drives a string of up to 10 white LEDs with a forward
voltage of 3.8V or less. 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 shutdown provide additional protection. A small
external capacitor and series resistor control soft-start and
loop compensation. Over-voltage detection protects the
SC4538 if the LED pin is floating or shorted to ground.
The SC4538 is available in an MLPD-8 pin 2mmx 2xmm
0.6mm package, with a rated temperature range of -40°C
to +85°C.
Typical Application Circuit
D
L1
2.8 to
5.5V
CIN
LX
IN
OUT
COUT
SC4538
Enable and
PWM dimming
EN
RISET
CCOMP
RCOMP
ISET
COMP
BL
GND
July 11, 2007
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