There's been a lot of soft-latched power switch circuits discussed here and elsewhere on the internet. However, I can't wrap my head around how to implement the following requirements:
- Battery powered (Lipo voltage range, LDO is used for noise reasons, device will measure in the millivolt range)
- Push to turn on (short hold to turn on would be acceptable too)
- While on, register button presses from MCU to handle soft power off
- Way for MCU to power system off
- Hold to force system off in case micro hangs
That last point is rather important as this circuit will go into a device where it would be very inconvenient/impossible for the user to disconnect the battery.