100mV Sense Voltage Offers Effective Regulation of LED Current

The LM3421/LM3423 devices are N-channel controllers designed for use with constant-current LED drivers. Adjustable high-side current sense, with a typical sense voltage of 100mV, allows for tight regulation of the LED current for increased efficiency.

Output LED current regulation is based on peak current-mode control with predictive off-time control. This controlmethod simplifies the design of loop compensation while providing inherent input-voltage feed-forward compensation.

The LM3421/LM3423 N-channel controllers include a high-voltage start-up regulator that operates over an input range from 4.5V to 75V. An internal PWM controller caters for adjustable switching frequencies of up to 2MHz, thus enabling compact solutions. The LM3423 also includes an LED output status flag, a fault flag, a programmable fault timer, and a logic input to select the polarity of the dimming output driver. Additional features include zero-current shutdown, a precision reference, and a logic-compatible DIM input suitable for fast PWM dimming.

With a full array of features, National’s LM3421 and LM3423 devices provide versatile high-voltage LED-driver control. They offer the capability to be configured in a buck, boost, buck-boost and SEPIC topologies; and provide an input operating voltage rating of 75V to illuminate LEDs in diverse applications.

 

FEATURES Input voltage range: 4.5V to 75V Current-sense voltage adjustable from 20mV High-side current sensing 2Ω MOSFET gate driver Dimming MOSFET gate driver Input under-voltage protection Over-voltage protection Less than 1µA shutdown current 50kHz PWM dimming Cycle-by-cycle current limit Programmable switching frequency

APPLICATIONS LED drivers Thermo-electric cooler drivers Constant-current regulation: Buck/boost Boost Flyback SEPIC

 

 

National Semiconductor / LM3421 & LM3423