Using p-chan mosfet to control power to MCU

[somespirit]

Hi there- I'm familiar with p-chan mosfets, but I've only ever used them with dedicated drivers or 12-15V source.

I'm looking to use a p-chan mosfet to enable one MCU to control power to a secondary MCU (see attached).

Will this switch adequately? i.e., will the pull up resistor from gate to source work okay at just 3.3V? The plan is obviously for the secondary MCU to turn ON when the primary MCU pulls it's output LOW.

thanks!

 

[MikeMl]

Depends entirely on the what the threshold voltage for the PFet is. To save quiescent current drain, you can leave out the 1KΩ, and up the gate-to-source resistor to ~100KΩ, or if port pin doing the switching has an active pull-up , leave it out...

If you can find a small PFet with a threshold of -1 to -2V, it will work. Otherwise, assuming you are switching about 50mA, use a PNP like a 2N3906, with a base resistor of about 1.5KΩ

 

[somespirit]

Thanks for the tips- I think I understand all that. Generally I've assumed the resistor on the MCU output is essential for protection, but I'm usually controlling motor driver stages... in this case, where the MCU output is rated for 20mA, and the secondary MCU can draw ~50mA max, the gate resistor really isn't needed?

The IRLML5103PbF has a gate threshold of -1.0V and Rds of 0.6Ohm, so it sounds way more than capable of what I need!

Edit: gave wrong product name for the part I have in mind