Automotive LED driver circuit using LT3486

　　The advantages of LEDs used in the center high-mounted brake lights (CHMSL) of cars include: faster reaching of set brightness, higher efficiency, longer service life, and the very small red LED array is easier to design and install; LEDs can reach set brightness in less than 1ms, so that drivers of cars behind can see the brake lights faster, thus reducing rear-end collisions. In contrast, traditional bulbs take up to 200ms to reach set brightness. Compared with incandescent lamps, LED lamps can reduce power consumption by up to 80%, thereby reducing fuel consumption of cars.

　　In order to maximize the performance of brake LED applications and extend their service life, the design of the "red light LED string" driver should be optimized in combination with the requirements of the automotive brake system. The LT3486 of Lingte Company is specially developed for such automotive applications. The LT3486 is a dual-boost DC/DC converter. The LED drive circuit composed of it is shown in the figure. After special design, it can drive up to 16 LEDs (8 in series for each converter) with a constant current from the 12-14V automotive bus. The LEDs connected in series can have the same LED current, thereby producing consistent brightness. If necessary, these two independent converters can also drive asymmetric LED strings.

　　The dimming of the 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 in the range of 200kHz to 2MHz. Its current detection circuit has a low feedback voltage (200mV), which reduces the power consumption of the current detection resistor, improves the circuit's operating efficiency, and has an output voltage limiting function when the LED is open.