R10 below - a 10k resistor straight between
GND. I can't come up with a reason why you'd want it to be there.
I've built several USB-powered microcontroller devices myself and I've never included this feature. Is this something I should have been doing, or did the designer just mess up? Any ideas?
My rambling thoughts about it:
- Normally I'd expect something like this in parallel with some capacitors you'd want to discharge, but the caps are all on the 5V/3.3V rails and the diode prevents R10 from draining them.
- If it were doubling as a fuse, I'd expect it to be in series with the protection diode, not tying the supply to ground.
- It's only about 0.5mA of always-on waste, but that's still more than the RP2040 itself draws in sleep mode.
- The connector is USB-C, but I don't know of any USB guidelines saying that gadgets should put a resistor between VUSB and GND.
- Looking at the schematic for the official Pico board, there's a GPIO attached to the VUSB through a 5k/10k pulldown divider, presumably to detect when the board is powered over USB. Maybe this designer looked at this and assumed the pulldown was required even without the GPIO?