I made a circuit that uses the DMP2305U P-Channel enhancement mode MOSFET. I connected the pin of the PIC microcontroller directly to the gate pin of the MOSFET. The purpose of this MOSFET to enable the power rail that an Xbee is connected to. I'm running the whole board off of a CR2477 lithium battery or external power with a TPS63001 buck/boost. The problem I'm running into is the CR2477 cannot run the Xbee, the PIC starts browning out and things just stop working. If I connect two AAs to the battery terminals, the board runs fine. From external power it runs just as fine. I can enable and disable the MOSFET by manipulating the pin on the PIC.
I believe the problem I'm running into is the buck/boost is providing 3.3V and the DMP2305U has a -0.7V drop which means there's not high enough voltage to run the Xbee which requires a minimum of 2.8V.
Assuming it's okay to run the MOSFET directly from the microcontroller, why might I have an issue running from CR2477 but not 2xAAs?
A friend pointed me to this write-up: Using MOSFETs in Load Switch Applications (AND9093 by On Semiconductor)
This tells me I need a transistor in front of the MOSFET. My success on external power and 2xAAs tells me I don't, that the 25mA I can source from the PIC pin is enough. Even if I put a transistor in front of it, I'd still have a voltage drop across the MOSFET, right?