Diodes ZXLD1321 - Manual

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
Note # : Using standard external components as specified under electrical characteristics. Efficiency is dependent upon
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
• Typical efficiency # >85%
• 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