The LED current for the external case LEDs is a little low. On the Checkmate A1500 Plus case, the orange HDD light is OK, but the green power light is a bit dim.

If the LED forward drop is 2V, with a 1 kΩ current limiting resistor, that's 1.3mA. With a 1.7V LED it's 1.6mA. With a green or blue LED at 3.2V, we'll only pass 100 µA!

PCs will typically provide 5V for the case LEDs. Maybe we need to generate 5V stand-by (e.g. TPS7A2450DBVR 5V 200mA LDO), as well as 3.3V. We can switch LEDs powered from 5V by setting the STM32 pins to be open drain (i.e. GND or High-Z).

This also has the advantage that:

a) We can power the keyboard from the 5V SB, for keyboard power-on.
b) It moves the LED current off the 30mA MAX1615 (or we could just make this LDO more powerful...)
c) It makes moving to an ATX power connector easier, because they provide 5VSB.

We would control an ATX PSU with a nPS_ON signal - pulling that line to ground to start the PSU.