1200

1400

1600

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2200

2400

2600

2800

2.8

3

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

4.8

5

V

TA = +25ºC

TA = -40ºC

TA = +85ºC

C032

I

IN

OUT

TEMP

SW

ENABLE

TORCH

TX

SDA

SCL

GND

1 2H

10 2F

10 2F

STROBE

LED2

2.7V to 5.5V

LED1

LM3646

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LM3646

SNVS962A – DECEMBER 2013 – REVISED NOVEMBER 2014

LM3646 1.5-A Synchronous Boost Converter With Dual High-Side Current Sources

1 Features

3 Description

The

LM3646

utilizes

a

4-MHz

fixed-frequency

1

•

High-Side Current Sources Allowing for Grounded

synchronous boost converter to provide power to dual

LED Cathode for Improved Thermal Management

1.5-A constant current LED sources. The high-side

•

> 85% Efficiency in Torch and Flash Modes

current sources allow for grounded cathode LED

•

operation providing flash current up to 1.5 A total. An

adaptive headroom regulation scheme ensures the

•

Accurate and Programmable Flash LED Current

LED currents remain in regulation and maximizes

from 24 mA to 1.5 A in 11.7-mA Steps

efficiency. The combination of dual LED driving

•

Accurate and Programmable Torch LED Current

capability, high LED current, small solution size and

from 2.5 mA to 187 mA in 1.5-mA Steps

high level of adjustability make the LM3646 perfect

•

Dual 1.5-A High-Side Current Sources for Dual

for camera phone LED flash and torch applications.

LED Drive

•

Hardware Flash and Torch Enables

interface. The main features of the LM3646 include: a

hardware flash enable (STROBE) input for direct

•

Hardware Enable Pin

triggering of the flash pulse, a hardware Torch enable

•

Soft-Start Operation for Battery Protection

(TORCH) for movie mode or flashlight functions, a TX

•

LED Thermal Sensing and Current Scale-Back

input which forces the flash pulse into a low-current

torch mode allowing for synchronization to RF power

•

Synchronization Input for RF Power Amplifier

amplifier events or other high-current conditions, an

Pulse Events

integrated comparator designed to monitor an NTC

•

VIN Flash Monitor Optimization

thermistor and provide an interrupt to the LED

•

1-MHz I²C-Compatible Interface

current, and a programmable input voltage monitor

•

I²C-Programmable NTC Trip Point

which monitors the battery voltage and can reduce

the flash current during low battery conditions. A

•

0.4-mm Pitch, 20-Bump DSBGA

hardware

enable

(ENABLE)

input

provides

a

hardware shutdown during system software failures.

2 Applications

The

4-MHz

switching

frequency,

overvoltage

Camera Phone LED Flash and Torch

protection, and adjustable current limit allow for the

use of tiny, low-profile inductors and (10-

μF) ceramic

capacitors. The device is available in a small 20-

bump DSBGA package and operates over the –40°C

to 85°C temperature range.

Device Information(1)

PART NUMBER

PACKAGE

BODY SIZE (NOM)

LM3646

DSBGA (20)

2.015 mm x 1.615 mm

(1) For all available packages, see the orderable addendum at

the end of the datasheet.

Typical Application Circuit

System Performance

1

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.