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

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Part Number: PCM1860

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

Regards,
Collin Wells
Precision ADC Applications

  • 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.

    If cost and space is an issue, you can use high value pull down resistors. The benefit of AC coupling the inputs to ground is power savings due to no DC current flow form the offset at the input pin to ground. A high value resistor will make this negligible anyway. You can get a single package part of 2, 4 or however many resistors you need for each unused input.  A separate resistor for each input is recommended so small common mode voltage differences between the inputs does not cause excessive current leakage between the two inputs.

    Regards,
    Collin Wells
    Precision ADC Applications

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