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Is PLL filter always needed in ADAU1978?

I started right now to design a board with the ADAU1978.

In the current design, a microcontroller generates all the I2S signals, included master clock.

The question is: can I supply ADAU with all the signals, disable the PLL and not install the PLL fiter? I wasn't able to find an answer on the datasheet or the forums.

Unfortunately, I am very limited in room, so any additional component counts.

Thanks.

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  • Hello kaibun,

    Sorry for the delay. 

    We really strongly recommend you use the PLL. Any jitter in your master clock will be translated to the audio so the PLL is really useful for that. Then it also develops the higher frequencies required for the internal filters. So if you bypass the PLL you will have to supply a higher master clock and we actually need to look up what you will need. My first guess is 512 x fs. What sampling rate do you plan to use? There will be a max master clock input. 

    The other detail is that the part was not characterized and tested with the PLL bypassed. 

    Dave T

  • Hi Dave, yes, the answer is quite late and we already discovered that PLL is needed.

    We have had additional trouble with phase synchronisation of two ADAU feeded with the same TDM signal. Thanks to the support of your colleague Salvatore Napolitano (Italy FAE) we selected frame clock instead than master clock, and the board worked fine.

    Giuseppe

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  • Hi Dave, yes, the answer is quite late and we already discovered that PLL is needed.

    We have had additional trouble with phase synchronisation of two ADAU feeded with the same TDM signal. Thanks to the support of your colleague Salvatore Napolitano (Italy FAE) we selected frame clock instead than master clock, and the board worked fine.

    Giuseppe

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