ZXLD1321 Boost mode DC-DC converter for LED driving with 1A output and current control Description The ZXLD1321 is an inductive DC-DC The feedback control circuitry inside the converter, with an internal switch, designed ZXLD1321 provides excellent load and current for driving single or multiple LEDs in series up regulation, resulting in very stable LED current to a total of 1A output current. over the useful life of the battery and over the full operating temperature range. Applications cover commercial environments with input voltages ranging from 1.2V to 12V. The LED current can be adjusted from 100% down to 10% of the set value by applying a dc The device employs a variable on and off voltage to the ADJ pin and down to 1% by time control scheme with adjustable peak applying a PWM signal to the ADJ pin. An on- switch current limiting and supports step-up chip LED protection circuit also allows output (Boost) mode and self-powering Bootstrap current to be reduced linearly above a operating modes, offering higher power predetermined threshold temperature using an efficiency and lower system cost than external thermistor at the TADJ pin. conventional PFM circuitry. External resistors set nominal average LED The device includes the DC-DC converter, a current and coil peak current independently. high-side current monitor and an NPN switching transistor to provide an integrated The device can be shut down by applying a solution offering small PCB size, competitive continuous low level dc voltage to the ADJ pin. 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. Features Applications 1.2V to 12V Input voltage range High power LED flashlights Up to 1A output current LED back-up lighting Typical efficiency >85% General LED lighting Bootstrap operation enables input voltage down to 1V Emergency lighting User-defined thermal control of LED output current using external thermistor High output current stability over input voltage and temperature 12A typical standby current LED current adjustable from 100% down to 2% Adjustable soft-start Drives up to 5 white LEDs in series 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 www.zetex.com Zetex Semiconductors plc 2008ZXLD1321 Pin connections (top-view) Package view Package DFN14 package (bottom view). 14-Pin DFN with exposed pad 45 chamfer denotes Pin 1 4mm x 3mm 0.50mm pitch 1.5W T =70C A Block diagram Issue 1 - January 2008 2 www.zetex.com Zetex Semiconductors plc 2008