Issue 1 - January 2008

1

www.zetex.com

© Zetex Semiconductors plc 2008

ZXLD1321

Boost mode DC-DC converter for LED driving with 1A

output and current control

Description

external component types and values. Higher efficiency is possible with alternative coils.

The

ZXLD1321

is

an

inductive

DC-DC

converter, with an internal switch, designed

for driving single or multiple LEDs in series up

to a total of 1A output current.

Applications cover commercial environments

with input voltages ranging from 1.2V to 12V.

The device employs a variable 'on' and 'off'

time control scheme with adjustable peak

switch current limiting and supports step-up

(Boost) mode and self-powering Bootstrap

operating modes, offering higher power

efficiency

and

lower

system

cost

than

conventional PFM circuitry.

The device includes the DC-DC converter, a

high-side current

monitor

and an

NPN

switching transistor to provide an integrated

solution offering small PCB size, competitive

cost/performance, high power efficiency of

DC-DC

conversion

and

maximum

LED

brightness/reliability. More importantly, it

retains design flexibility to add customer

specific features.

The

feedback

control

circuitry

inside

the

ZXLD1321 provides excellent load and current

regulation, resulting in very stable LED current

over the useful life of the battery and over the

full operating temperature range.

The LED current can be adjusted from 100%

down to 10% of the set value by applying a dc

voltage to the ADJ pin and down to 1% by

applying a PWM signal to the ADJ pin. An on-

chip LED protection circuit also allows output

current

to

be

reduced

linearly

above

a

predetermined threshold temperature using an

external thermistor at the TADJ pin.

External resistors set nominal average LED

current and coil peak current independently.

The device can be shut down by applying a

continuous low level dc voltage to the ADJ pin.

Features

•

1.2V to 12V Input voltage range

•

Up to 1A output current

•

•

Bootstrap operation enables input voltage

down to 1V

•

User-defined

thermal

control

of

LED

output current using external thermistor

•

High output current stability over input

voltage and temperature

•

12µA typical standby current

•

LED current adjustable from 100%

down to 2%

•

Adjustable soft-start

•

Drives up to 5 white LEDs in series

Applications

•

High power LED flashlights

•

LED back-up lighting

•

General LED lighting

•

Emergency lighting