LED signal light driver reference design

Circuit description

This application note introduces a linear LED driver solution for driving 6 strings of LED signal lights, each string containing 4 LEDs in series. Each string of LED loads has an independent anode contact, and the cathodes are connected together. The circuit is powered by a car battery with a minimum voltage of 10V and a maximum voltage of 28V, capable of providing 350mA current to each string of LEDs.

Due to the common cathode architecture, the current-sense resistor must be placed at the anode end of the LED string. The maximum common-mode voltage at the current-sense input of the LED driver ( MAX16836 ) is limited to 4V, so the voltage across the current-sense resistor must be level-shifted and referenced to ground to comply with the driver's requirements. A pair of PNP transistors converts the voltage from the LED current-sense resistor into a voltage referenced to GND, which is fed into the current-sense pin of the MAX16836. The following equation provides the calculated values ​​for R1, R2, R3, and R4 (U1 in the circuit diagram):