1 Features

? Quad independent led current source

programmability

? Accurate and programmable LED current range

from 0.525 mA to 2 A

? Optimized flash LED current during low battery

conditions (IVFM)

? > 85% efficiency in torch mode (at 100 mA) and

flash mode (at 1 A to 2 A)

? Grounded cathode LED operation for improved

thermal management

? Dual hardware strobe enable (STR1, STR2)

? Synchronization input for RF power amplifier pulse

events (TORCH/TX)

? Hardware torch enable (TORCH/Tx)

? Dual remote NTC monitoring (TEMP1, TEMP2)

? Fixed output voltage mode

? 1-MHz I2C-compatible interface

– (I2C Address = 0x65)

2 Applications

? Camera phone white LED flash

? Digital still cameras

? Barcode scanners

? Handheld data terminals

3 Description

The LM3645 is a quad LED flash driver that provides

a high level of adjustability within a small solution size.

The LM3645 utilizes a synchronous boost converter to

provide power to the quad 2A constant current LED

sources. The quad 256 level current sources provide

the flexibility to adjust the current ratios between

LED1, LED2, LED3 and LED4 with each driver

capable of delivering a maximum of 2A. An adaptive

regulation method ensures the current sources remain

in regulation and maximizes efficiency.

Features of the LM3645 are controlled via an I2Ccompatible

interface. These features include: dual

hardware flash pins and a hardware torch or Tx

interrupt pin (STR1, STR2 and TORCH/TX), and

dual NTC thermistor monitors. The device offers

independently programmable currents in each output

leg to drive the LEDs in a flash or movie mode (Torch)

condition as well as a fast turn-on and turn-off IR

Mode.

Two switching frequency options, overvoltage

protection (OVP), and adjustable current limit allow for

the use of tiny, low-profile inductors and 10μF ceramic

capacitors. The device operates over a –40°C to

+85°C ambient temperature range.