I'm working on a battery powered project, and I'm trying to implement an 'auto-off switch' (not sure if there's a more suitable term, if so by all means let me know) with the idea that a momentary button press switches power on from my battery to the rest of the circuit, and straight away the micro will hold a signal connected to the switching circuit in the desired state. Then if the micro detects no activity for some period of time it can set the signal to Hi-Z the signal and everything turns off.
I'm pretty sure I've got a very simple and straight-forward way of achieving this (though I'm open to suggestions) my only query now is whether to switch high or low...
So the circuits are as follows, this is the high sided switching version:
R1 is simply to keep the circuit off when the switch isn't pressed or uC Sig is Hi-Z. When the button is pressed it will pull the gate of Q1 low and thus current will flow - great. Then the micro that uC Sig is connected to will drive uC Sig low to keep the power on after the button is released. When I want to switch off I simply set uC Sig back to Hi-Z.
And now the low-sided switching version:
So this is basically an exact replica of the high sided version only G2 is an n channel MOSFET, the gates pulled low by default to ensure it's off, and the button and uC Sig will pull and drive high respectively.
Essentially what I'd like to know are the general pros and cons between high-sided and low sided switching, as well as any general advice on the matter and which way you guys would go if it were up to you.
My gut instinct is telling me that the high-sided switching method would be better since it actually removes power from the load rather than ground, and also as the Rds on of the FET will cause the two grounds either side to be slightly different from one another in the low sided version. (Of course the same applies to the actual voltage for the high sided version, but the Vcc being slightly less seems like less of an issue than the ground levels being different).
Also, the battery is a Li-Po unit that will range from +3.0V to +4.2V if that's of any significance...