SC4540 Datasheet, PDF (1/15 Pages) Semtech Corporation – High Effi ciency Boost Converter for up to 10 LEDs

POWER MANAGEMENT
Features
„ Input voltage range — 4.5V to 12V
„ 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 — 38V (minimum)
„ Under-voltage lockout (UVLO)
„ Thermal shutdown
„ Shutdown current — <0.1μA (typical)
„ Ultra-thin package — 2 x 2 x 0.6 (mm)
„ Lead-free package, WEEE and RoHS compliant
Applications
„ DSLR, DSC, and Video Cameras
„ Portable media players
„ Set-top boxes
„ Personal navigation devices
SC4540
High Efficiency Boost Converter
for up to 10 LEDs
Description
The SC4540 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. The wide input voltage range of the SC4540
makes it ideal for use with dual-cell Li-ion powered
applications.
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 38V (guaranteed) to drive up to 10
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
SC4540 if the BL pin is floating or shorted to ground.
Typical Application Circuit
The SC4540 is available in an MLPD-8 pin 2 x 2 x 0.6 (mm)
package, with a rated temperature range of -40°C to
+85°C.
L1
D
5 6 μH
1 μF
LX
C OUT
4.5 to 12V
IN
OUT
C IN
2.2μF
SC 4540
Enable and
PWM
dimming
R IS E T
CCOMP
RCOMP
1 .2 7 k Ω
47nF
EN
IS E T
COMP
BL
GND
July 18, 2008
© 2008 Semtech Corporation
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