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PCM2906C: HID Interface Configuration for headphone jack

Adam Bierman
Intellectual 710 points
Part Number: PCM2906C
Other Parts Discussed in Thread: PCM2902,

I would like to use the PCM2906C to accept two input channels and output 4 signals. My customer is reporting that the Behringer UCA202, based on the PCM2902, is able to offer a headphone jack that he believes is interfaced to the HID pins that allows the user to listen to both the input and output at the same time. I wanted to ask if that was possible on the PCM2906C using these pins, or how one might connect to the IC to accomplish this.


I believe the PCM2902 in the Behringer UCA202 supports this, and it seems to have a similar interface set so I was thinking it would be a similar configuration. I am also worried that's what is being reported to me is not accurate and the internals of that UCA202 are muxing signals together in a way I'm not aware of and not actually using the HID pins on the codec.

  • 0
    TI__Guru 62745 points

    Hi Adam,

    The PCM2906 features stereo ADCs (2-channel) and stereo DACs (2-channel), so you would need to externally design a configuration for 4xOutputs with the available connections.  

    Could you draw a simple block diagram of what you're looking to accomplish on the headphone jack?  Provided the jack has separate input/output connections then the system would be able to support both on the same jack.

  • 0 in reply to Collin Wells
    Intellectual 710 points

    I misspoke on the 4 channels, we take the two unbalanced outputs and put them through a TPA3132 amplifier which has +/- output channels for 4 signals.

    With the PCM2906C what I've been asked to do is something like:

     

    Where the idea is the HID interface can allow you to listen to what is coming in or what is going out of the codec, from the codec.  I could add an external configuration and switches but the customer is convinced this output interface from HID is possible on the PCM2902 and thinks it also is on the PCM2906, is there a way to configure the HID in this way?

  • 0 in reply to Adam Bierman
    TI__Guru 62745 points

    Hello,

    The HID pins are digital inputs, not outputs and with it being a hardware controlled device I don't imagine there are any special ways (like a hidden register write) to make this happen.  That said, if the customer is convinced they've done this before then perhaps it's possible but if so it's outside of our knowledge of the product's operation.

  • 0 in reply to Collin Wells
    Intellectual 710 points

    Hello,

    Ok, that's what I figured, so what I'm going to do is send the I/O to a relay that switches between the input and output channels, put those through an amplifier/buffer and connect to a jack connector so we can switch and listen to the signals that are going directly into the codec.  Do you see any problem with that? The amp/buffer is not yet installed in this schematic but this gives you an idea what I am thinking (All the input and output conditioning is done on other schematic pages).  

  • 0 in reply to Adam Bierman
    TI__Guru 62745 points

    Hi Adam,

    That looks like it would work.  The connections are always physically separated and the configuration depends on the SW9 switch settings.

  • 0 in reply to Collin Wells
    Intellectual 710 points

    Thanks Collin, we went ahead and added an output buffer stage to this circuit, just like the one in the demo circuit on the output lines, to separate the J37 connector from the codec when it's not in use so the connections aren't hanging and the connector is grounded; we think this will offer an improvement on the audio and I figured I would make sure you didn't see us introducing something that would make this configuration fail: