[FAQ] PCM1860: What should I do with unused inputs on the PCM1860 and other devices in the PCM186x family?

The datasheet for the PCM186x devices states in Section 9.3.1 Analog Front End that nothing should be connected to unused inputs.  

If having floating issues is a challenge in your system, then the recommendation for unused inputs on TI's Audio ADCs and CODECs is to provide an AC termination to GND through a ~0.47uF capacitor to prevent noise-pickup on an un-terminated input.    The analog inputs have a DC bias on them so they should not be shorted directly to GND.  The ~0.47uF capacitor provides an open-circuit for the DC bias inside the device, but provides an AC short to GND for proper termination and noise-reduction.