I am controlling the voltage of a 3.6V lithium battery with a MCP112-250 (I know it is 3V but I have a diode in series with my battery).
And the output is connected to the gate of a N-channel MOSFET, IRFB7430PbF according to this schematic :
The MCP112 is doing his job by toggling his ouptup from high to low.
When Vin>2.5V I have my MCP112 output high and I have 2.5V at Vout of the LDO, and when Vin<2.5V I have my MCP112 low but I don't have 0V as expected but aproximately 1.2V when Vin=2.2V.
My circuit is not shut down as expected… Theoretically when I have a 0V on the gate of a N-channel it has to be "open" so my system is off.
But why is this working like there were no MOSFET ?
EDIT:
It seems I have some current leaking from somewhere… Because when the MOSFET is removed I have Vout=~2V …But from where ? I used a GND power plane on my board. Is it possible that current is leaking between the pads and the power plane ?
Best Answer
SOLUTION:
If you are "cutting" the ground make sure you are measuring your output from where you realy want to measure it !
In my case I was measuring Vout from Vout of the LDO and the negative pole of the battery, so when Vin>2.5V Vout=2.5V, but when Vin<2.5V the MOSFET disconnect the ground of the battery from the rest of the circuit so between Vout and the negative pole of the battery there is a remaining voltage. But if you are measuring between the 2 pins of J1 or J2 you should see 0V, but if you are measuring from Vout on J1 or J2 and the negative pole of the battery you are not measuring what you are expecting... So this is why I got strange voltage on my multi-meter...
In short:
When you are measuring a voltage with your multi-meter make sure to measure with the good ground reference !