High-side P N FET driver resistor

[Pha5e]

In a high side driver configuration consisting of a P-type FET for the pass function and an N-type FET for the switching function, how do I calculate the value of the pull-up resistor which connects the gate of the pass transistor to the source (input supply)?

 

[crutschow]

It's mainly a function of the switching speed you need. That resistor has to charge the gate capacitance of the P-MOSFET to turn it off, so the smaller the resistor, the faster it can turn off. Of course the smaller the resistor, the more power is dissipated when the P-MOSFET is ON. So the trade-off is between turn-off speed and power.

 

[Pha5e]

Is there a formula I can use to calculate an optimal value for the resistor based on the figures in a datasheet?

Most application notes I read seem to mention between 1k and 10k?

 

[crutschow]

As I said, it depends upon the switching speed you need. Do you know what that is? What is the P-MOSFET you want to use?

 

[Pha5e]

It's just to power on a wireless module from a micro-controller. The switching speed does not need to be high.

 

[crutschow]

It's just to power on a wireless module from a micro-controller. The switching speed does not need to be high.

In that case you can use a high value of resistor to minimize power if you want, limited mainly by leakage from the P-MOSFET gate and the off leakage of the N-MOSFET. You could likely use 100kΩ or even higher.