If an input gets a voltage level that is above the Vdd, the output is going low
instead of staying at Vdd potential.
° Would it be possible to get some infos on the background of this behavior..?
° Due to the fact that the AD822 is a classic device... could there be an
alternative with the expected behavior (e.g. AD8626)?
It is important to distinguish between over-voltage protection (i.e. the
ability of an IC to withstand input voltages greater than the power supply
voltage) and output phase reversal (a part specific phenomenon, where the
output is inverted as the input common mode approaches or exceeds the supplies).
The AD822 is not damaged when the input voltage exceeds 0.2V provided the input
current is limited to less than 10mA. However, the output may go into phase
reversal when the input exceeds the supplies.
In any case, the absolute maximum ratings supersede anything else in the
datasheet and should be respected at all times.