I'm using the MAX6650 operating from 3.3V to control a 5V fan.
I have questions on the MOSFET selection for this application.
1) In order for the MOSFET to work properly in this application it seems it would need one a relatively low gate-to-source conduction threshold Vgs(th) since the voltage to the GATE pin will be 3.3V maximum. Say 2V or less. Is this correct? Does the exact value matter as long as it's below say 2V? In this application is the MOSFET operating as a switch or in the linear region? I'm confused at how the circuit works in closed-loop and how we get different voltages at the FB pin?
2) What determines the possible value range of voltage at the FB pin (the low side voltage to the fan)? It seems ideally I want it to be able to range from 5V (fan would be off) all the way down to 0V (fan would see full 5V). What effect does the Vgs(th) have on this possible range.
3) For a 5V fan, it seems for the MOSFET any Vgs and Vds(br) above say 8V would be fine?