Issue 2 - April 2008
www.zetex.com
© Zetex Semiconductors plc, 2008
ZXLD1321EV2 USER GUIDE
DESCRIPTION
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
•
12µA typical standby current
•
Adjustable Soft-Start
•
Drives up to 5 white LEDs in series
APPLICATIONS
•
High power LED flashlights
•
LED back-up lighting
•
General LED lighting
ORDERING INFORMATION
ORDER NUMBER
ZXLD1321EV2
Please note evaluation boards
are subject to availability and
qualified leads.
TYPICAL APPLICATION CIRCUIT
