ZXLD1322 Datasheet, PDF (1/18 Pages) Zetex Semiconductors – Buck/boost mode DC-DC converter for LED driving with 700mA output and current control

ZXLD1322
Buck/boost mode DC-DC converter for LED driving
with 700mA output and current control
Description
The ZXLD1322 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 700mA output current.
Applications cover input voltages ranging
from 2.5V to 15V. Depending upon supply
voltage and external components, this can
provide up to 12W of output power.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and operates in Buck/
Boost mode, offering higher power efficiency
and lower system cost than conventional PFM
buck/boost 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
ZXLD1322 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. 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
• 2.5V to 15V Input Voltage Range
• Up to 700mA output current
• Typical efficiency^# >80%
• 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
• Capable of driving 3 LEDs in series
Applications
• High power LED flashlights
• LED back-up lighting
• General LED lighting
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.
Issue 1 - January 2008
1
© Zetex Semiconductors plc 2008
www.zetex.com