I am using transistor NXP PSMNOR9 http://www.nxp.com/documents/data_sheet/PSMN0R9-25YLC.pdf
and I have it in an OR power controller circuit using a TI TPS2413 http://www.ti.com/lit/ds/symlink/tps2413.pdf - Page 18
When I apply 5V to the source and have the gate grounded then I am getting 4.5V on the drain.
I also have the transistor by itself simply hooked up to a power supply with 5V on the Source and ground on the Gate and the Drain is at 4.5V.
My prototype PCB works the way that we intended, but we wanted to add a way to drop out one of the multiple power supplies by forcing the gate low. This looks like it will still work by doing this. However, I was under the impression that bringing the gate voltage to 0V would thus bring the drain to 0V.
I understand this is an unconventional use of a MOSFET, and I can not find any information on why it is performing this way in this use.