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SC4540EVB Datasheet(PDF) 1 Page - Semtech Corporation |
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SC4540EVB Datasheet(HTML) 1 Page - Semtech Corporation |
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1 / 15 page  © 2008 Semtech Corporation POWER MANAGEMENT 1 Typical Application Circuit 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 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 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. 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. OU T LX BL CIN 4.5 to 12V IN EN ISET GN D COM P E nable and PW M dim m ing L1 D C OUT SC 4540 1 μF 56μH 2.2μF RISET CCOM P 1.27kΩ 47n F RCOM P July 18, 2008 |
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