I want to digitize 8 floating AC voltages (50Hz) with Vref (pin10) as common signal. Can I do that?
If I understand your question correctly, you would like to apply an AC voltage to each of the ADC inputs. These signals cannot float - there must be some specific DC level. Are you asking if that DC level can come from the Vref voltage?
The Vref is 2.5V, so you could use that to derive a DC level. Be sure to buffer it, because it is not a low-impedance output. As long as the AC + DC levels do not exceed the input range of the ADC this will work.
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