SAADC differential mode voltage

[julienh]

Hi,

I would like to measure the voltage generated by a Thermoelectric generator. The voltage vary between -250mV and 250mV depending on the temperature gradient. 

If the generator is floating (not referenced to the circuit ground) and that I connect + and - of the generator directly to 2 analog input of the NRF52 and measuring in differential mode, is that ok and would have been able to measure the full range without causing any physical dommage to the chip? 

Thank you 

[Carsten Wulff]

That depends, you have to ensure that the voltage on either pin (+ or - ) does not exceed the absolute maximum rating of the device, you can find that in the product description. 

Other than that I would be concerned with the amount of current that your thermo generator could produce, particularly if the load impedance varies significantly.

As long as the absolute max ratings are ok, then I would expect the SAADC to work in differential mode. 

I would consider if adding a cap from + and - to ground provides some ac short to ground, so the common mode does not vary to much at high frequencies.