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, overvoltage
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 micro-SMD package.