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PCM2706C: Schematic review

Martin Harmia
Prodigy 30 points
Part Number: PCM2706C
Other Parts Discussed in Thread: PCM2706

Hello,

I have a schematic with PCM2706C, where it functions as a USB <-> I2S bridge, that would need a review. There has been some debate on the size of the capacitors by the crystal, and if they should be smaller or bigger. The load capacitance of the crystal is 20 pf, so to achieve a 5 pf capacitance for the board, the caps should be even 30 pf. Is it possible to use larger (20-30pf) capacitors by the crystal, or do they need to be smaller?PCM2706C Schematic.pdf

  • +1
    TI__Mastermind 25220 points

    Hi Martin,

    In theory the CL is calculated from the following equation:

    CL= {(Ca.Cb)/(Ca+Cb)}+Cp  ,

     so based on your requirement of CL and your estimate of parasitic/stray Cap you can calculate Ca and Cb

    The user guide  for PCM2706 EVM is using ECS-120-18-5P  with 15P caps.  

    If you want to use a different crystal, you can estimate Ca and Cb  based on above to get to the ballpark requirement.

    Regards,

    Arash