LED matrix driving with junction temperature sensing :

LEDs are used in headlights. There are many LEDs working for different sections. Those LEDs can be arranged as a matrix or distributed within a headlight to combine the light later on the road. To turn off a section like the high beam this means to turn off a group of LEDs or single ones. Therefore a number of switchable channels are required. To keep the costs and component count low LEDs are operated in a string with the same drive current and are turned ON and OFF and dimmed by PWM when bridging sections of them with a switch. Even the full string can be deactivated by the bypass switches taking the full drive current. The schematic shows such an example with two channels of a string of ten LEDs.

The parts are very small, some integrated in multi part packages and of low cost - if the channel count is low a discrete solution offers low cost and hi drive capabillity. The Nexperia BUK6D56-60E offers 4A constant current in a tiny SMD package and is a very good switch for bridging high power LEDs.

The switching transistion of a MOSFET is hard and can create EMC or exceeding the peak drive current of an LED. There is a feedback of a R-C combination to the gate at the turn on transition to smooth the peak current. It is needed because of the discharge current of the buck output cap, which can flow over the active channel of the string.
A single operation of one active channel by delaying the phase enables the ADC measurement at turned of Buck regulatore at low discharge current out of the cap to determine the junction temperature of the active LEDs.