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.