Multiple LED curcuit
Power is going to be delivered via a 12V car battery and has to be brought down to MCU voltages 3V3 or 5V.
... TLC5951DAP ...

From the datasheet:


LED Power-Supply Voltage up to 15 V


There is no need to have the LEDs connected to the regulator. Have them connected directly to the 12V supply and let the driver handle it. As long as you use the HTSSOP-38 package with the PowerPAD soldered you should be able to withstand at least 2.5W which is within the (12V − 2V) ⋅ 10mA ⋅ 20 = 2W maximum power handling required.