> > A possible cause is that you are seeing the charge from the ADC's
> > internal sampling capacitor. Another possible cause is leakage caused
> > by an analog input clamping a voltage above the supply rail.
>=20
> I would hope that wasn't the case.  Shouldn't there be at least a buffer
> amplifier between the capacitor and the switch?

Nope, not when you look at the simplified schematics they put in the data s=
heet and family manuals. That is one reason why there is a significant rest=
riction on signal source impedance to maintain the ADC accuracy.

--=20
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