1 Features

1• Dual Independent 1.5-A LED Current Source

Programmability

• Accurate and Programmable LED Current Range

from 1.4 mA to 1.5 A

• Torch Currents up to 360 mA (LM3644TT)

• Flash Timeout Values up to 1.6 seconds

(LM3644TT)

• Optimized Flash LED Current During Low Battery

Conditions (IVFM)

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

Flash Mode (at 1 A to 1.5 A)

• Grounded Cathode LED Operation for Improved

Thermal Management

• Small Solution Size: < 16 mm2

• Hardware Strobe Enable (STROBE)

• Synchronization Input for RF Power Amplifier

Pulse Events (TX)

• Hardware Torch Enable (TORCH/TEMP)

• Remote NTC Monitoring (TORCH/TEMP)

• 400-kHz I2C-Compatible Interface

– LM3644 (I2C Address = 0x63)

2 Applications

• Camera Phone White LED Flash

• Digital Still Cameras

• Fire-Alarm Notification

• Emergency Strobe Lighting

• Intruder Alert Notification

• Barcode Scanners

• Handheld Data Terminals

3 Description

The LM3644 is a dual LED flash driver that provides

a high level of adjustability within a small solution

size. The LM3644 utilizes a 2-MHz or 4-MHz fixedfrequency

synchronous boost converter to provide

power to the dual 1.5-A constant current LED

sources. The dual 128 level current sources provide

the flexibility to adjust the current ratios between

LED1 and LED2. An adaptive regulation method

ensures the current sources remain in regulation and

maximizes efficiency.

Features of the LM3644 are controlled via an I2Ccompatible

interface. These features include:

hardware flash and hardware torch pins (STROBE

and TORCH/TEMP), a TX interrupt, and an NTC

thermistor monitor. The device offers independently

programmable currents in each output leg to drive the

LEDs in a Flash or Movie Mode (Torch) condition.

The 2-MHz or 4-MHz switching frequency options,

overvoltage protection (OVP), and adjustable current

limit allow for the use of tiny, low-profile inductors and

10-μF ceramic capacitors. The device operates over

a –40°C to +85°C ambient temperature range.