Tiny High-Efficiency Driver Handles 10 White LEDs

Packed into an 8-lead, 2- by 3-mm DFN package, the LT3591 high-efficiency white-LED driver from Linear Technology Corp. features an integrated Schottky diode, eliminating both the cost and space normally need for this external component. A unique high-side LED current-sense topology enables the LED cathode to be connected directly to ground, creating a single-wire current source. The LT3591 can drive up to 10 white LEDs from a single Li-Ion cell at efficiencies above 78%. It switches at 1 MHz, allowing the use of a tiny inductor and capacitors while keeping switching noise out of critical RF bands. The combination of the LT3591’s high efficiency, low noise, and extremely small total-solution footprint makes it well-suited for handheld applications requiring multiple white LEDs for backlighting.

To ensure uniform LED brightness, the LT3591 acts as a constant current source, delivering the same current to each white LED, regardless of fluctuations in the LED’s forward voltage drop, which varies with temperature, manufacturing tolerances, and age. The LT3591 also uses True Color PWM dimming to offer a wide dimming range of up to 80:1. Additional features include output voltage limiting when LEDs are disconnected and ±5% reference accuracy.