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PCM1864: clocking interactions and requirements

Tim Burnett
Prodigy 40 points
Part Number: PCM1864

I'm planning on non-audio frequency sampling, and have read everything I can find (including this forum) on clocking interactions in the PCM1864, and am still vague on some of the interactions. I am planning on using master mode 4-channel TDM with an input SCK of 38.4MHz, desired sample rate is either 50kHz or 75kHz (either is fine). By the data sheet BCK can be 6.667 MHz max, but I'm not sure of max-min or norminal clock settings for DSP1, DSP2, or the ADC. I know LRCLK_div should be 256 since I'm in TDM mode. I don't think I need the PLL (the input SCK is very high quality). 

Q1: Since BCK is 6.4MHz max in master mode, does that mean my max sample rate is ~26kHz (6.667MHz/256)?

Q2: Should DSP1 and DSP2 clocks always be equal?

Q3: Should the ADC clock always be slower than the DSP clocks? By some factor? Divided from the same source? 

Q4: What are the maximum frequencies for the ADC and DSP clocks? 

Q5: Any recommendations for my clock setup?

Thanks!

Tim Burnett

  • 0
    Prodigy 40 points
    After lots of experimentation with register values, I have had luck with the following (please double check that these are safe). Input SCK is a high quality 38.4MHz.

    addr=val (all on page0)
    x0b=x4b
    x0c=x01
    x20=x10
    x21=x0
    x22=x0
    x23=x5
    x25=x0
    x26=x2
    x27=xff

    This gives 50kHz data (4 channels TDM), which is a desirable data rate for me, but BCK is 12.8MHz (~half the min BCK period value in datasheet figure 47). However the output waveform on BCK looks great, for the single device tested. Since I'm not sure what's driving the datasheet minimum BCK period specification, I wonder if this will cause trouble for me later? Can you please let me know, if in my particular use case the 12.8MHz BCK is OK? I have also tried 19.2MHz BCK (setting addr x26 to 1) and that waveform looks quite good as well.

    Regards,
    Tim
  • 0 in reply to Tim Burnett
    TI__Guru 57800 points

    Hi, Tim,

    Welcome to E2E, Thanks for your interest in our products!.

    I will take a look to your questions and will get back to you as soon as possible.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 40 points

    It's been a couple days since your reply. Is anyone looking into this? 

    Thanks, Tim