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| SC4538 |
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 SEMTECH
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POWER MANAGEMENT 1 High Efficiency Boost Converter for up to 10 LEDs Typical Application Circuit July 11, 2007 OUT LX BL CIN 2.8 to 5.5V IN EN ISET GND COMP Enable and PWM dimming RISET CCOMP L1 D COUT RCOMP SC4538 Applications White LED Display Backlight Driver Smartphones and PDAs Cellular Handsets MP3 and Portable Media Players DSC, GPS, Satellite Radio, Game Players SC4538 Features 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 Description 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. |
