Microcontroller soft power button

[Things]

Hi all,

I'm working on designing a product that needs to be as physically small as possible. It will incorporate a microcontroller, and have a single button for accessing various modes. It'll have a small inbuilt LiPo battery for power - but the it occurred to me, how do I turn it on and off. Being a LiPo, it'd need to have no draw in the off state, but I also don't really have the room for a separate switch.

I've had this idea before, but I couldn't really seem to get it to work. Basically I'd have the switch connected directly to the battery positive, as well as an I/O pin. When pressed, it'd send power into the boost converter, which in turn would power up the microcontroller. I could then use a transistor on another I/O pin to keep it "latched" while the micro is running (or an enable pin on the boost converter, if it has one). This would also make it very easy to incorporate a hard low voltage cutoff to protect the LiPo.

However I seem to recall thoughts about this not working for some reason. Said product is just for fun, so things like the microcontroller accidentally rebooting and killing it's own power isn't a big deal.

Cheers,
Dan

[8086]

https://www.eevblog.com/forum/projects/an-idea-for-soft-power-with-no-quiescent-loss/

[Mad ID]

Hi all,
I'm working on designing a product that needs to be as physically small as possible. It will incorporate a microcontroller, and have a single button for accessing various modes. It'll have a small inbuilt LiPo battery for power - but the it occurred to me, how do I turn it on and off. Being a LiPo, it'd need to have no draw in the off state, but I also don't really have the room for a separate switch.

I've had this idea before, but I couldn't really seem to get it to work. Basically I'd have the switch connected directly to the battery positive, as well as an I/O pin. When pressed, it'd send power into the boost converter, which in turn would power up the microcontroller. I could then use a transistor on another I/O pin to keep it "latched" while the micro is running (or an enable pin on the boost converter, if it has one). This would also make it very easy to incorporate a hard low voltage cutoff to protect the LiPo.

However I seem to recall thoughts about this not working for some reason. Said product is just for fun, so things like the microcontroller accidentally rebooting and killing it's own power isn't a big deal.

Cheers,
Dan

It will work. You have a PFET on the power signal. The pushbutton pulls the gate of the PFET low and the system start running. The pushbutton has an NFET in parallel which the MCU turns on as soon as it boots. When you want to shut down, just release the NFET. Whola.