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PCM5122: Output impedance when muted

Tommy S��rensen
Prodigy 20 points
Part Number: PCM5122

Hi

When using the XSMT pin to mute the PCM5122 I have experienced that the output impedance is different when the DAC is muted and when it is not. I have tried to sweep the output impedance (using a BODE 100) and get an impedance reading of around 90ohm when the XSMT pin is low (muted) and <1 ohm when the XSMT pin is high (unmuted). What is the reason for this change in impedance?

I'm also using an LC filter in the output of the DAC - instead of the recommended RC filter. Will this be an issue for the DAC or create any instability?

Best regards

Tommy

  • 0
    TI__Guru 53623 points

    Hi Tommy,

    When the output is enabled, you are basically seeing an amplifier output (<1Ω makes sense).  When you assert XSMT, the output amplifier is eventually powered down/disabled.  In power down, the output is a bit higher impedance.  When disabled, I believe the output is connected to ground through a high-ish impedance.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 20 points

    Hi Paul

    Thank you for the explanation on the output impedance.

    Do you have any experience regarding the LC output filter?

    Regards

    Tommy

  • 0 in reply to Tommy S��rensen
    TI__Guru 53623 points

    Hi Tommy,

    I have not seen too many questions about using an LC output filter.  Do you have specific questions or schematic?

    Thanks,

    Paul