Carl, There isn't a big issue tying an unused input to ground. The original motivation for giving this guidance was that there may be a modest rise in the ADC input leakage current (with the used input) with the unused input tied to ground. This is more of an issue with the series input filtering resistance using 24-bit ADCs and the LSB size is under 1uV. However, it shouldn't be a problem on this device. For the open unused pin, the multiplexer in the device should isolate the input from noise. Joseph Wu
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