DescriptionThe 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 onchip LED protection circuit also allows output current to be reduced linearly above a predetermined threshold temperature using an external thermistor at the TADJpin. 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 and Benefits• 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