Santa Clara, Calif. National Semiconductor Corp. says it has introduced the industry's first common-anode, current-mode, high-brightness light-emitting diode (LED) driver with pulse-width modulation (PWM) dimming. The LM3433, part of National's PowerWise energy-efficient product family, drives high-power, high-brightness LEDs in backlighting, projector and solid-state lighting applications.
National said the LM3433 LED driver opens the way for high-reliability LEDs to be used in large-screen LCD TV backlighting applications where a common-anode approach offers a thermal advantage. LEDs also can be used in today's shrinking “pocket projector” designs for a wider color gamut, higher reliability and longer life expectancy than the ultra-high performance (UHP) lamps used today.
The LM3433 is a constant on-time DC-DC buck (step-down) constant-current regulator. It outputs a negative constant current for lighting high-power, high-brightness LEDs. The negative voltage option allows the anode of the LED to be tied directly to the ground-referenced chassis for maximum heat sink efficacy. The short constant-on-time architecture allows the use of small external passive components and no output capacitor, said National.
Two current control modes modulate LED brightness. An analog current control input is provided so the LM3433 can be adjusted to compensate for LED manufacturing variations. The other current control is a logic-level dimming input for PWM control of LED brightness. The PWM functions by shorting out the LED with a parallel switch, allowing high PWM dimming frequencies up to 40 KHz. Additional features include thermal shutdown, VCC under-voltage lockout and logic-level shutdown mode. The LM3433 is offered in a 24-pin LLP package.
National Semiconductor , www.national.com