The LM3508 is a synchronous boost converter (no externalSchottky diode required) that provides a constant current output.It is designed to drive up to 4 series white LEDs at 30mAfrom a single-cell Li-Ion battery. A single low power externalresistor is used to set the maximum LED current. The LEDcurrent can be adjusted by applying a PWM signal of up to100kHz to the DIM pin. Internal soft-start circuitry is designedto eliminate high in-rush current at start-up. For maximumsafety, the device features an advanced short-circuit protectionwhen the output is shorted to ground. Additionally, overvoltageprotection and an 850kHz switching frequency allowfor the use of small, low-cost output capacitors with lowervoltage ratings. During shutdown, the output is disconnectedfrom the input preventing a leakage current path through theLEDs to ground. The LM3508 is available in a tiny 9-bumpchip-scale micro-SMD package.