Diodes ZXLD1320 - Manual

Issue 1 - January 2008 1 www.zetex.com
© Zetex Semiconductors plc 2008
ZXLD1320
Buck mode DC-DC converter for LED driving with
1.5A 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 ZXLD1320 is an inductive DC-DC
converter, with an internal switch, designed
for driving single or multiple LEDs in series up
to a total of 1.5A output current.
Applications cover both commercial and
automotive environments with input voltages
ranging from 4V to 18V. Depending upon
supply voltage and external components, this
can provide up to 24W of output power.
The device employs a variable 'on' and 'off'
time control scheme with adjustable peak
switch current limiting and operates in the
step-down (Buck) operating mode, 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
ZXLD1320 provides excellent load and current
regulation, resulting in very stable LED current
over the full operating voltage and 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 'Power-OK' (POK) output flag remains high
during normal operation, but switches low if the
switch transistor remains on for more than
500
μ s. This provides indication of a low battery,
or fault condition. The POK output may be used
to drive an LED or the input of an MCU.
The device can be shut down by applying a
continuous low level dc voltage to the ADJ pin.
Features
• Step-down LED driver
• 4V to 18V input voltage range
• Up to 1.5A output current
• Typical efficiency # > 85%
• User-defined thermal control of LED
output current using external thermistor
• High output current stability over input
voltage and temperature
• 12 μ A typical standby current
• LED current adjustable from 100%
down to 2%
• Adjustable soft-start
• Power 'OK' flag output
• Capable of driving 4 LEDs in series
Applications
• Low voltage halogen lamp replacement
with LEDs
• High power LED flashlights
• LED back-up lighting
• General LED lighting
• Automotive lighting