1 Features

1? Grounded Cathode LED Operation for Improved

Thermal Management

? 1.5-A High-Side Current Source for Single LED

? Accurate and Programmable LED Current from

46.9 mA to 1.5 A

? > 85% Efficiency in Torch Mode (at 100 mA) and

Flash Mode (at 1 A to 1.5 A)

? Small Solution Size: < 20 mm2

? LED Thermal Sensing and Current Scale-Back

? Soft-Start Operation for Battery Protection

? Hardware Enable Pin

? Hardware Torch Enable

? Hardware Strobe Enable

? Synchronization Input for RF Power Amplifier

Pulse Events

? VIN Flash Monitor Optimization

? 400-kHz I2C-Compatible Interface

? I2C-Compatible Programmable NTC Trip Point

? 0.4-mm Pitch, 16-Pin DSBGA Package

2 Applications

Camera Phone LED Flash

3 Description

The LM3556 is a 4-MHz fixed-frequency synchronous

boost converter plus 1.5-A constant current driver for

a high-current white LED. The high-side current

source allows for grounded cathode LED operation

providing flash current up to 1.5 A. An adaptive

regulation method ensures the current source

remains in regulation and maximizes efficiency.

The LM3556 is controlled via an I2C-compatible

interface. Features include: a hardware flash enable

(STROBE) allowing a logic input to trigger the flash pulse, a hardware torch enable (TORCH) for Movie

Mode or flashlight functions, a TX input which forces

the flash pulse into a low-current Torch Mode

allowing for synchronization to RF power amplifier

events or other high-current conditions, and an

integrated comparator designed to monitor an NTC

thermistor and provide an interrupt to the LED

current. With a fast 1-μs transition from 0 mA to

46.9 mA, the TORCH input pin can be used to

develop custom LED current waveforms.

The 4-MHz switching frequency, overvoltage

protection and adjustable current limit allow for the use of tiny, low-profile inductors and 10-μF ceramic

capacitors. The device is operates over a ?40°C to

+85°C temperature range.