Hey guys, I'm designing a controller at the moment, and I've got 2 devices that need to switch the same MOSFET, one being a battery monitoring IC and the other an ATMega. My plan was to use an NPN resistor on the MOSFET's gate, that will allow the ATMega to pull the MOSFET's gate to ground, and hold it there so the battery IC can't bring it back up again (With a gate resistor of course).
Problem is, the battery chip will remain connected and powered at all times, but the uC won't, so what'll happen is when the uC gets turned off, the NPN transistor can no longer pull the MOSFET gate down, and the MOSFET will turn on.
So, what I'm asking, is can I use a pullup resistor on the NPN transistor so it's on while the uC isn't, then have the uC pull that down, without having to use a 2nd transistor?
My thoughts were the ATMega doesn't have any internal pulldowns, so the answer would be no, but a friend insists otherwise, saying if you connect a LED between 2 digital pins and write them HIGH and LOW, the LED will work, implying it's pulling to ground.