LED Driver Offers Adjustable High-Side Current Sense for Efficient Operation

The LM3421/LM3423 high-voltage LED driver controllers can be configured in a buck, boost, buck-boost, flyback or Single-Ended Primary Inductance Converter (SEPIC) topology.

Adjustable high-side current sense with a typical sense voltage of 100mV (20mV minimum) allows for tight regulation of the LED current with high efficiency. Output LED current regulation is based on peak current-mode control with predictive off-time control. This eases the design of loop compensation while providing inherent input-voltage feed-forward compensation.

The LM3421/LM3423 includes a high-voltage start-up regulator that operates over an input range of 4.5V to 75V. The internal PWM controller is designed for adjustable switching frequencies of up to 2MHz, enabling compact solutions. Additional features include zero-current shutdown, a precision reference, a logic-compatible DIM input suitable for fast PWM dimming, cycle-by-cycle current limiting, and thermal shutdown.

With the addition of a few small and inexpensive external components, a slow-shutdown or fade-out feature allows the LEDs to transition slowly to the off-state which is particularly useful in automotive interior lighting applications. The LM3423 also includes an LED-output status flag, a fault flag and a programmable fault timer for advanced fault diagnostics, plus a logic input to select the polarity of the dimming output for more flexible dimming configurations.

 

FEATURES 2% internal reference voltage (1.235V) High-side current sensing 2Ω MOSFET gate driver Dimming MOSFET gate driver Input under-voltage protection Over-voltage protection <1µA maximum shutdown current 50kHz PWM dimming

APPLICATIONS Automotive interior lighting LED Drivers Constant-current regulation

 

National Semiconductor / LM3421/LM3423