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PCM1681: Proper power components for 2 PCM1681 on the same board

Nicolas LEROY20
Prodigy 60 points
Part Number: PCM1681
Other Parts Discussed in Thread: TPS54232

Hi,

I am looking for a proper power design to power 2 DAC PCM1681 located on the same board. The board is powered with 12V and digital audio signals come from another board. 

I started with a TPS54232 to get 5V out of the 12V input and then I use LP2985-33DBVR to get 3v3 from 5V. 

That works but I think that there might be a better design for performance and cost.

Any idea ?

Thanks,

Nicolas

  • 0
    TI__Guru 53283 points
    Hi Nicolas,

    I think in general you are on the right track, you I would suggest using the SMPS to create a lower, intermediate supply - maybe 6V, then using another low noise LDO with high PSRR to create the 5V supply. For example the TPA7A90 has only 4.7uVrms in the 10-100kHz range.

    www.ti.com/.../datasheet

    Please let me know if that answers your question.
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 60 points
    Hi Paul,
    Thanks for your answer. Would you choose the TPS54232 to get 6V ? What regulator would you use for 3v3 ? TPA7A90 also ? Would you connect it to 6V from SMPS or to 5V from LDO ?
    Any special consideration regarding AGND and DGND ? Ferrite bead ?
    Thanks,
    Regards,
    Nicolas
  • 0 in reply to Nicolas LEROY20
    TI__Guru 53283 points
    Hi Nicolas,

    I think the TPS54232 is a good choice. The TPA7A90 would also be a good fit for the 3.3V supply, but the VDD is slightly less critical from a noise perspective than AVCC as it is the digital supply. But unless you are targeting a very low cost solution, the 7A90 should be good. You can derive the 3.3V from the 5V and get even better PSRR, but as I mentioned VDD is somewhat less critical. I think the real variable would be the total current your system needs for the 5V and 3.3V supply. If the 3.3V supply is connected to the 5V supply, its current comes from the 5V current 'budget'.

    Figure 36 in the PCM1681 PDS describes the recommended grounding scheme, which advises that the DGND and AGND of the PCM device be both considered Analog Ground, then use a single point grounding scheme with the rest of the digital components. Ferrite bead may valuable if you are using extensive digital components (generating high frequency noise).

    Please let us know if this resolves your issue.

    Thanks!
    Paul