Christian,
I don't have any specific data on the internal protection diodes for the ADS131E08. However generally they are setup up like this:
As the input goes above the AVDD, current is shunted through the diode to AVDD. As the input goes below AVSS, current goes from the pin through the diode and is shunted to AVSS. These diodes will limit the voltage that AINx can be pulled above or below the supplies.
Often, we do use series resistance to limit the amount of current that the diode will see. In the Absolute Maximum Table, we say that the maximum input current is ±10mA. If you know that there may be a sustained overvoltage, then you can calculate the approximate resistance you want to limit the input current to a particular level. I'd note that the 10mA is the absolute maximum and you'd want to make sure the input protection doesn't hit that level or there may be damage to the device.
However, I would recommend additional input protection diodes. Even in the datasheet, we show additional input protection in the typical application:
If you happen to be working with electricity meters, there are a couple of TI designs that show how input circuitry is set up including protection. While they use the ADS131M04, the input measurement and protection may be applicable to your design. They show some thermistors and TVS diodes used to protect the input (along with series resistance alone).
https://www.ti.com/tool/TIDA-010036
https://www.ti.com/tool/TIDA-010037
Regardless, look them over and let me know if you have additional questions.
Joseph Wu
