I'm working on an android multigauge for cars based of a pic microcontroller. Some inputs from sensors are not fed by my circuit so after stumbling upon this thread: http://www.microchip.com/forums/m612024.aspx, I had to make some changes to the circuit to be able to respect the fact that an input can't have more voltage then the voltage supply + 0.3V. So this was fixed with a schottky diode array on the input and a tvs diode on the supply line.
But I started to check the specs on other chips on my circuit. The AD8495 on it's datasheet on page 3 calls for an input voltage range of -Vs - 0.2V to +VS - 1.6V. http://www.analog.com/media/en/technical-documentation/data-sheets/AD8494_8495_8496_8497.pdf
Am I correct in thinking that if my circuit is not powered but is grounded (fuse blown or something) and that there is voltage on the inputs (+in to -in) then it's not safe? Thermocouple input voltage is tiny but if Vs is 0V and the input is 30mV, that is more than 0V - 1.6V... And if I want to protect against a wrong connection, let's say someone connects 12V by mistake on the input. Then even if Vs is 5V and if I have diodes protecting the inputs, voltage would be limited to about 5.2V and that would still be above VS - 1.6V...
Am I correctly understanding this? And if so, what would be the proper way to make sure that the input is always at Vs - 1.6V max?