LM3508_08 Datasheet, PDF (1/14 Pages) National Semiconductor (TI) – Synchronous Magnetic Constant Current White LED Driver

March 6, 2008
LM3508
Synchronous Magnetic Constant Current White LED Driver
General Description
The LM3508 is a synchronous boost converter (no external
Schottky diode required) that provides a constant current out-
put. 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 protec-
tion 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 micro-SMD package.
Features
■ ^{Drives 4 Series White LEDs with up to 30mA}
■ ^{>80% Peak Efficiency}
■ ^{Up to 100kHz PWM Brightness Control}
■ ^{Accurate ±5% LED Current Regulation across V}_IN ^range
■ ^{Internal Synchronous PFET (No Schottky Diode}
Required)
■ ^{True Shutdown Isolation}
■ ^{Output Short-Circuit Protection}
■ ^{17.5V Over-Voltage Protection}
■ ^{Internal Soft-Start Eliminates Inrush Current}
■ ^{Wide Input Voltage Range: 2.7V to 5.5V}
■ ^{850kHz Fixed Frequency Operation}
■ ^{Low Profile 9-Bump Micro-SMD Package (1.514mm x}
1.514mm x 0.6mm)
Applications
■ ^{White LED Backlighting}
■ ^{Handheld Devices}
■ ^{Digital Cameras}
■ ^{Portable Applications}
Typical Application Circuit
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