I am designing a circuit that should convert a unipolar differential audio signal using an ADC. The signal varies between 200mV - 28V peak to peak and I'm planning to use the TI PMC6020 ADC that accepts differential inputs up to 10V RMS.
Unfortunately, the circuit may accidentally be connected to a bipolar signal (-20V to 20V peak to peak at maximum) during installation (this condition could last for several minutes). The ADC only tolerates -0,3V negative input, so there should be some protection against continuous negative voltage.
My first idea was to use a Zener diode connected from the ADC input to ground, but that will clip the signal at -0,7V.
A normal diode in series will not work either, as the voltage drop will affect the reading of the signal when the amplitude is low.
Any suggestion how to clamp the negative voltage in this case? Are there any ideal diode circuits that can be used for this purpose?
I have no split rails available, only 3.3V.