Get rid of the MAX16054

[sp5wwp]

The chip is completely unnecessary. STM32 can run in low-power mode and be woken up using an external trigger (key press). There's no need for an expensive power switch.

[RoganDawes]

I was looking at your schematic for inspiration for a Blackberry Q5 replacement PCB, and was wondering how SW1 was used. Interesting to see that you concluded that it was unnecessary. I'm planning to use an ESP32-P4 (when more readily available), which also has a low-power mode, so hopefully should be ok as well. It might make more sense to have a BMS chip with undervoltage lockout, though?

[sp5wwp]

The button itself is necessary, it's the MAX16054 that is expensive and might be replaced with something else or removed completely, having the button routed directly to the MCU.

[RoganDawes]

Ah, I guess I misunderstood! I was thinking that it doesn't really make sense to (be able to) cut power to the microcontroller without involving the microcontroller, and giving it an opportunity to save its state if needed. Enabling power to the microcontroller, sure. But cutting it abruptly seems unlike most operating modes we are used to these days (hold power for some seconds to trigger a shutdown, or similar).

Seems like connecting external power should be enough to trigger power on (perhaps after a delay), and holding a power button for an extended period would work to enable/disable power to the microcontroller, but also give the microcontroller an opportunity to react to the button press if wired directly to a GPIO?