Battery monitor circuit

Hardware
1

Hi all,

I wonder whether anyone can suggest what’s going on here? Probably something obvious, but… I’ve been playing with a design based on the battery monitoring circuit shown on https://electricimp.com/docs/hardware/power_story/

The idea being to turn off the resistor network necessary for battery voltage sensing, except when it’s actually needed, to reduce current consumption. I think I’ve incorporated the design into my schematic correctly (see attached).

Q7 happily turns on and off under the control of PIN_A. However, the voltage on the gate of Q1 never gets above 0.4V (this with 3.6V on the battery rail). I am deeply confused by this - does anyone have any suggestions? I’m clutching at straws, at the moment.

Cheers,

Gavin

2

My guess: check the pinout of your FETs are correct (ie, that D,G,S are on the pins that you think they are). Never trust libraries :wink:

3

Yeah, I thought I had my level of suspicion turned up high enough, but evidently not! I’ll check again…

4

For future reference: yep, the D & S pins on the transistor I was using were swapped. Some leg-twiddling and all is good.