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I'm using a PCM5102A DAC in a project and I've noticed that when the IC goes to sleep (>1 second without data on the I2S bus) there is some errant switching noise audible via the amp.

If I connect the R/L channels to analog ground, everything sounds great. My question is:

How can I automatically ground the R/L channels when there is nothing coming from the analog output of the DAC?

A monostable has been suggested to me, but I feel like that might be too complex of a solution for this.

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    \$\begingroup\$ There's not many logic/temporal circuits that are simpler than a monostable, so your "feel like that might be too complex" is pretty meaningless. Use a monostable multivibrator. Since you've already got knowledge of how to solve the problem, I'm not sure what you're asking? \$\endgroup\$ – Marcus Müller Feb 26 '19 at 16:27
  • \$\begingroup\$ @MarcusMüller - Thanks for your reply! I simply wanted to know if there was an alternative solution that made more sense. \$\endgroup\$ – t3ddftw Feb 26 '19 at 16:31
  • \$\begingroup\$ What's driving the DAC with I2S? If it's coming from a microcontroller or similar which you have control of, you can set a pin and drive a relay or similar to ground them. \$\endgroup\$ – Colin Feb 26 '19 at 16:56
  • \$\begingroup\$ @Colin - The DAC is driven by a BC127 Bluetooth module, so I have no access to its pins, unfortunately. \$\endgroup\$ – t3ddftw Feb 26 '19 at 17:02
  • \$\begingroup\$ Note that pop-free muting is non-trivial, in large part because most modern audio circuits operate with a DC bias. You either retain the DC bias, in which case what you want is not ground, or you remove it, in which case you need to do so slowly enough that it does not get through any following high pass filter (ie capacitive stage coupling). Pop-free mute/shutdown is typically a first-page-of-data-sheet selling point for amplifiers which have it. Or perhaps you can build some go-to-sleep sequencing into your code, walking the DC level and then using a GPIO to drive a switch. \$\endgroup\$ – Chris Stratton Feb 26 '19 at 17:22
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If you look at datasheet history, they deleted mentions about intelligent clock detection and pop-free operation. So the external muting may need to be detected from clocks being absent and muting externally before DAC goes to sleep. And to remove external muting after DAC has woken up but before DAC unmute ramp.

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  • \$\begingroup\$ Good eye! I currently plan to tie AGND to the analog output channels via a FET. That way, when the charge pump goes low (shutdown) I can sink those lines to AGND. \$\endgroup\$ – t3ddftw Feb 26 '19 at 21:20

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