High side power switch with P-channel MOSFET

[Wilson__]

Is this circuit correct? 

It switches on Li cell 4.2V to resistor voltage divider that feeds ADC to read cell voltage  state of charge. 

Switch off after ADC measurement to avoid constant draining of Li cell.

Many thanks

[ajb]

Yeah, that looks fine.  I wouldn't really call it a "power" switch, since even though it's switching a power supply connection it isn't really powering a load in the usual sense.  It's just a signal switch in this case.  But if it were a higher power application, R2 requires some consideration -- at 100k it will result in a fairly slow turn-off of M2, which could be problematic.  For switching a voltage divider, though, it's perfectly fine.

[Peabody]

Excuse the hand drawing, but below is a somewhat simpler circuit.  It works even if D4 is at a lower voltage than the battery.  It basically replaces the NMOS with a capacitor.

[Wilson__]

Many thanks.

Yes, the resistor determines speed of (dis)charge of gate.  We did not read that part of data sheet before, any headup on how these are specified?

Many thanks