You are adding mux Rdson to Ntc value, so you would have to
do an error analysis to see if performance meets your goals.
If you use ohmmeter tool you would be able to see delta values
between various thermistor paths, a contributor to chan-chan error.
That is exactly what I have in mind. That is why I hoped to find the application note i found it in.
I hope there is a way to switch the analog input from these pins in such a way that I can measure the analog voltage OUTSIDE of the digital output. That is also why I use digital outputs because they have a lower output resistance than analog outputs.
Attached - better version of my diagram. I use the Output Enable to switch between channels
Looking at GPIO specs, Vddio 3.3, 3 mA sink, Vol <= .4 V. So inferred
Rdson <= 13.3 ohms.
So thats an appreciable error in light of "typical" characteristics below.
And of course there is a strong T dependence of Rdson.
You could always dedicate a pin and using current source measure its
Rdson and subtract that out from reading. Analysis of all errors would be
Food for thought. Regards, Dana.