PWM

Control

Thermal

Shutdown

+150

IN

I

2

C

Interface

Error

Amplifier

Slope

Compensation

SDA

SCL

Control

Logic/

Registers

GND

OUT

LED

STROBE

TORCH/TX

SW

80 m:

80 m:

Over Voltage

Comparator

Soft-Start

4 MHz

Oscillator

UVLO

Input Voltage

Flash Monitor

OUT-VHR

Current Sense/

Current Limit

LM3642

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SNVS891H – SEPTEMBER 2012 – REVISED SEPTEMBER 2015

7 Detailed Description

7.1 Overview

The LM3642 is a high-power white LED flash driver capable of delivering up to 1.5 A into a single high-powered

LED. The device incorporates a 4-MHz constant frequency-synchronous current-mode PWM boost converter and

a single high-side current source to regulate the LED current over the 2.5-V to 5.5-V input voltage range.

minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is above

the LED voltage + current source headroom voltage, the device does not switch and turns the PFET on

LED is dropped across the current source.

The LM3642 has two logic inputs including a hardware Flash Enable (STROBE) and a Flash Interrupt input

(TX/TORCH) designed to interrupt the flash pulse during high battery current conditions. Both logic inputs have

internal 300-k

Ω (typical) pulldown resistors to GND.

current levels, changing the Flash Timeout Duration and changing the switch current limit. Additionally, there are

flag and status bits that indicate flash current time-out, LED failure (open/short), device thermal shutdown, and

7.2 Functional Block Diagram

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