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PCM5102A-Q1: Maximum voltage swing

Theodore Salmon
Intellectual 350 points
Part Number: PCM5102A-Q1
Other Parts Discussed in Thread: PCM5102A, TS5A22364

Hello,

Unfortunately, I wasn't able to find this answer in the device datasheet. I'm adding an analog mute circuit to the PCM5102A because the XSMT functionality doesn't work like I need it to (I need L/R tied to AGND when the device is muted or otherwise not operational). I have decided to use the TI TS5A22364 SPDT analog switch which has negative voltage signaling ability for the task, but I'm not sure what the maximum voltage of the PCM5102A is (2.1v is what it's rated at, but what are the real world possibilities here). Additionally, I need to know what the voltage swing is.

I have also considered simply tying AGND to the normally connected pins of the TS5A22364 and leaving the normally closed pins N/C'd. That way, when music is not playing and the control pins on the switch are LOW, AGND will be tied to the L/R channels and I won't have to worry about passing audio through the TS5A22364.

Your input and information are greatly appreciated :).

-Ted

  • 0
    TI__Guru 52683 points
    Hi Ted,

    The output will nominally have the range of ±3V. (2.1VRMS*2√2 = 5.939Vpp). We specify a max gain error of 7%FSR, so you can estimate that as 5.939V*1.07 = 6.36Vpp.

    That may be too large for the SPDT switch, but you can try attenuating the output in your audio source, or possibly use a resistor divider to scale the output.
    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Intellectual 350 points

    Hi Paul,

    Thanks, as always, for your detailed response. I'd rather not attenuate the audio source or scale it, and 6.36Vpp is way too much for the TS5A22364 to handle.

    Can you think of any potential issues if I move forward with my plan to connect AGND to the Left / Right audio channels when the TS5A22364 is in its normally connected state (i.e. when the DAC is disabled). I tested this in the real world and it passed my quality requirements, but I would like to make sure I'm not overlooking something.

    Thanks!
    -Ted

  • 0 in reply to Theodore Salmon
    TI__Guru 52683 points
    Hi Ted,

    The issue is that the input and output pins should have ESD protection diodes, which will turn on if the potential on the pin exceeds the supply voltage by a certain amount (the forward voltage of a diode, usually). Based on the Absolute maximums table, you can see that the show the max/min of VDD+0.5 and VDD-5.5V. I think on this device they do something clever to let the inputs go lower than GND, but that does not change that the voltage on the COM should not exceed these maximums. Even though you are using not passing the audio through the switch, it is still connected to the COM pins. Those ESD diodes can still turn on if the supply exceeds these values.

    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Intellectual 350 points

    Paul,

    Thanks for the explanation, that makes total sense. I wasn't aware of the ESD diodes on the outputs.

    Back to your original suggestion, the TS5A22364 stipulates a max voltage of VDD-5.5V or VDD + 0.5 as an absolute maximum.

    Using the voltage divider formula, we find that (6.36v * 6.43kOhms) / (1kOhms + 6.43kOhms) = 5.5v, which places the Vpp right at the max swing of 5.5v. This a possible swing of 2.75v to -2.75v, which means I need to supply VCC on the TS5A22364 with 2.75v.

    Given that I am not as well versed in Audio signaling as I should be, my assumption is that the voltage divider would not impact quality, but may lower audible volume on the receiver end. Is that correct?

    If so, then I will go the way of the voltage divider, since I can't find a compatible SPDT switch for this DAC.

    EDIT: Fixed my misunderstanding & add additional info.

    -Ted

  • 0 in reply to Theodore Salmon
    TI__Guru 52683 points
    Hi Ted,

    The output scaling will not change audio quality, only the amplitude (slightly quieter). If you attenuate the signal a bit more, you might be able to supply the TS5A64 with the same 3.3V supply as well.

    Thanks,
    paul
  • 0 in reply to Paul_Frost
    Intellectual 350 points
    Paul,

    Perfect -- Thanks again for your insight!

    One last bonus question, if you don't mind: Will the voltage divider have any issues scaling the negative voltage?

    Thanks,
    -Ted
  • 0 in reply to Theodore Salmon
    TI__Guru 52683 points
    Nope, the PCM can source and sink current.