The LM3508 is a synchronous boost converter (no external Schottky diode required) that
provides a constant current output. It is designed to drive up to 4 series white LEDs at 30mA from
a single-cell Li-Ion battery. A single low power external resistor is used to set the maximum LED
current. The LED current can be adjusted by applying a PWM signal of up to 100kHz to the DIM pin.
Internal soft-start circuitry is designed to eliminate high in-rush current at start-up. For
maximum safety, the device features an advanced short-circuit protection when the output is shorted
to ground. Additionally, over-voltage protection and an 850kHz switching frequency allow for the
use of small, low-cost output capacitors with lower voltage ratings. During shutdown, the output is
disconnected from the input preventing a leakage current path through the LEDs to ground. The
LM3508 is available in a tiny 9-bump chip-scale DSBGA package.
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