analogWriteResolution explanation please

I struggling with how analogWriteResolution fits into the PWM equation. Looking at the docs I see this:

NOTE: The resolution also affects maximum frequency that can be used with analogWrite(). The maximum frequency allowed with current resolution can be checked by calling analogWriteMaxFrequency().

I’ll be using a PID library to drive the fan based on temp so higher resolution would be helpful but not sure what I should be aiming for. The PWM signal needs to be 25kHz which seems to be an out of the box capability since 6.0. So given I need a 25kHz PWM signal what resolution should I be using? I could also use some advice on a simple on/off circuit so the fan can be completely turned off as the fan will run at 30% as long as it has power. I found this but it seems like overkill since I only need on/off

Details on the project:
This for an enclosure for my 3D printer that will have NeoPixels, temp sensors, VOC/smoke sensors, couple of relays and a 12V 4-Pin PWM Fan. The signal to the fan needs to be 25kHz as per the Intel PWM fan specs (Intel 4-Pin PWM Spec). I have selected a 140mm Noctua fan as they are the quietest I could locate (Fan Datasheet). I have a power supply/regulator that provides 3.3v, 5v, 12v and a fourth adjustable regulator (Multi-Output Power Supply/Reg).

I’m not sure you need to play with resolution.
I’d think the default 8bit (0~255 pulse pause ratio) should do, and still allow for your 25kHz PWM frequency.

Only if analogWriteMaxFrequency() returns a frequency too low for your needs, you should need to reduce the resolution.

I don’t quite follow this tho’

If you set your PWM to 0 duty cycle the power should be off anyway, or what am I missing?

It is a 4 Pin fan and the Intel spec states in absence of 30%+ duty cycle the fan will run at 30%. I will have to control the 12v power to cut it off.

I see, in that case a simple FET controlled by a second digital pin should do the trick.

I might have misspoke here. Will take some testing but it appears there are three possible compliant implementations of the spec. Only one type forces rotation at a manufacturer defined minimum RPM I’ll have to do some testing to figure out which type my fan is. It is also entirely possible that 0 duty cycle will result in 0 RPM for all implementations as the wording in the spec isn’t exactly clear on that scenario. Just wanted to clarify in case someone else happened upon this thread.

I’ll update the thread when I get it working but the 4pin PWM fans should be a much easier to use option that also includes a “tach” so you can monitor actual RPM vs just the duty cycle of the PWM output.