Automotive LED driver circuit diagram using LT3486

The advantages of LED when used in automobile central high-mounted brake lights (CHMSL) are: it can reach the set brightness faster, has higher efficiency, longer service life, and its very small red LED array is easier to Designed and installed; the LED reaches the set brightness in less than 1ms, allowing drivers of cars behind to see the brake lights faster, thus reducing rear-end collisions. By comparison, traditional light bulbs can take up to 200ms to reach set brightness. Compared with incandescent lamps, the power consumption of LED lamps can be reduced by up to 80%, thereby reducing the fuel consumption of cars.

In order to maximize the performance of brake LED applications and extend their service life, the design of the "red LED string" driver should be optimized based on the requirements of the automotive braking system. Linear Technology's LT3486 was developed specifically for such automotive applications. LT3486 is a double boost DC/DC converter. The LED driving circuit composed of it is as shown in the figure. After special design, it can drive up to 16 LEDs (each 8 converters can be connected in series). Connecting LEDs in series allows them to have the same LED current, resulting in consistent brightness. If required, these two independent converters can also drive asymmetric LED strings.

The dimming of these two LED strings can be independently controlled through their respective CTRL pins, and the internal PWM dimming system can extend the dimming range to 1000:1 by providing PWM signals to their respective PWM pins. The operating frequency of the LT3486 can be set with an external resistor, and its range is 200kHz ~ 2MHz. Its current detection circuit has a low feedback voltage (200mV), which reduces the power consumption of the current sensing resistor, improves the working efficiency of the circuit, and has an output voltage limiting function when the LED is open.