Regarding the outpus being on when VCC has no voltage:
This is due to the way the pull-up resistors are hooked up and the fact we're using N channel FETs to drive more N-channel FETs.
Basically with no input on the gate of the DMN2075U's (the ones matching outputs 1-4), they are left in their open state. This means that the gate on the IRLB8743's gets all of +VGATE, switching it on.
This basically means that the existing Dual FET arrangement is broken by design if the 3.3v supply fails. :/
This is due to the way the pull-up resistors are hooked up and the fact we're using N channel FETs to drive more N-channel FETs.
Basically with no input on the gate of the DMN2075U's (the ones matching outputs 1-4), they are left in their open state. This means that the gate on the IRLB8743's gets all of +VGATE, switching it on.
This basically means that the existing Dual FET arrangement is broken by design if the 3.3v supply fails. :/