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PCM5122: PCM5122 and TPA6130A2: Schematic review and questions

Adam Heinrich
Prodigy 20 points
Part Number: PCM5122
Other Parts Discussed in Thread: TPA6130A2

Hello,

I am designing a board with PCM5122 and TPA6130A2 (both powered from a shared 3.3V line) and I'd like to ask for a schematic review. Moreover, I have a few questions regarding usage of the chips:

  • PCM5122 datasheet says I2C pull-ups shall be 1k to 2k for 5V bus level, what is the recommended value for 3.3V bus level?
  • PCM5122 datasheet recommends LPF of 470R+2.2nF at the line out output; I have added it for both the line out output and the line which goes to the amplifier. Is this necessary? Can I share the filter for both signals?
  • Can I connect PCM5122 pins such as MODE2 and XSMT directly to Vdd?
  • For a single-ended input, the datasheet of TPA6130A2 recommends connecting it to IN-. However, I'd like to avoid having inverted signal -- is it OK to connect it to IN+ instead and connect IN- to ground? Is the DC blocking capacitor on the grounded input necessary?
  • Do I need to add any filter between digital and analog voltage lines? If so, what would you recommend?

Thank you,
Adam Heinrich

ioboard_audio-Audio.pdf

  • 0
    TI__Guru 55043 points
    Hi Adam,

    1. The pullup values are really more dependent on the line capacitance. I think you should be fine with 2kΩ, but check out this article for more detailed explanations: www.ti.com/.../slva689.pdf
    2. They can share the same filter.
    3. You can connect them directly to DVDD, but I would recommend that you use XSMT as a voltage supervisor as described in section 10.3 of the PDS.
    4. You can ground IN- to use a single ended input, but I recommend that you keep the capacitor so that the input of the TPA has matching impedance.
    5. You could implement a ferrite bead between DVDD/CPVDD and AVDD to filter some of the noise from the higher frequency switching.

    Other comments: SCK should be grounded if you are using 3-wire mode.
    As you have a capacitor on VCOM, I assume you are using the device in VCOM mode. This will result in slightly worse AC PSRR performance, but better DC PSRR, as the output will scale based on the AVDD voltage so there is no possibility of headroom issues. If you are confident that the DC value of the AVDD voltage is stable, then I suggest you use VREF mode, where the pin is grounded.
    It may be valuable to add a DC blocking cap on the lineout connections as well, to remove any DC loads from the DAC.


    Thanks,
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 20 points
    Hi Paul, thank you very much for your comprehensive answer!

    The capacitor on VCOM is there by mistake, I want to use the default VREF mode. Thank you for pointing this out.