Hi Mario, I'm glad to hear that you resolved the issue, and thanks for sharing your solution! There is no issue with grounding the unused input pins; however, for measurements that utilize the internal PGA, then you'd want to make sure that these pins are not biased too closely to AVDD or AVSS. Just like an op-amp, the internal PGA outputs cannot drive all the way to the supply rails so you want to try to bias these pins closed to a mid-supply voltage. For offset calibration or noise testing, I would recommend shorting the inputs together, but instead of shorting to ground, short to ~2.5V. This can be accomplished by (internally with the MUX, or externally) connecting the inputs to AINCOM and enabling the VBIAS level-shifter.
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