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DIR9001: DIR9001 accepting 192KHz sample rate

Nebojsa Zdravkovic
Prodigy 90 points
Part Number: DIR9001
Other Parts Discussed in Thread: PCM1794A, DIX4192, DIX9211

I finished my project with DIR9001 and PCM1794A and to my surprise, DIR9001 worked just fine with 24bit/192KHz audio signals from SPDIF, although it's rated as 96KHz in the datasheet. I also verified this with the scope. How can this be? It's running on PLL, with CKSEL pulled to gnd.

  • 0
    TI__Mastermind 23050 points

    Hi Nebojsa,

    DIR9001 will extract the sample rate from the biphase mark encoded SPDIF stream and set the LRCLK accordingly. It was not designed to operate at that high of a frequency, but I suppose it's feasible that it could work, though we do not guarantee specified performance at that rate. There may also be potential loop filter stability issues if you have not adjusted the loop filter values. Datasheets don't necessarily specify the only conditions over which the part will work, but the only conditions over which we guarantee the part will work.

    Best,

    Zak  

  • 0 in reply to Zak Kaye
    Prodigy 90 points

    Тhanks for the reply. I did not modify loop filter values and I did not see any stability issues so far. Which values would you recommend for covering full range of sampling frequencies, from 44 till 192KHz please?

    I do however see problems in DIR9001 startups occasionally - but this happens with 44KHz sampling rate as well.

  • 0 in reply to Nebojsa Zdravkovic
    TI__Mastermind 23050 points

    Hey Nebojsa,

    I have limited information available on the loop filter stability, but I can tell you that the recommended values in the datasheet for the loop filter components are actually optimized for fs = 28kHz. Why this was done I'm not sure, and as you have observed it is certainly still capable of higher rates.

    For your case I would recommend reducing the values of C1 and C2 in the loop filter by 4x and increase R1 by 2x. This should give you the same level of stability with wider loop gain in the PLL. I still can't guarantee anything about the performance up to 192kHz because this is outside of specification.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    Prodigy 90 points

    Thanks, but it does not seem to make any difference. When it works, it works with wide tolerance off filter components. It seems that parts that have markings AFRT do not work with 192Khz, and those marked CTHD work just fine. Can you explain what these markings mean as I could not find any documentation about it?

  • 0 in reply to Nebojsa Zdravkovic
    TI__Mastermind 23050 points

    Hi Nebojsa,

    Device markings typically refer to the lot number of the device and die revision if appropriate. There have not been any die revisions to this part though. What you will find is that all of these parts will meet datasheet spec, but with process variations some parts may be able to perform better than spec. If you intend to rely on this then you would have to implement your own screening process, and keep in mind that we do not guarantee the parts will meet other specs under conditions we do not test. We also do not have the ability to guarantee which lot material you will receive, as this will depend on where you order from and what inventory is on hand.

    You could do this with your own screening process, but I still would not recommend it. I would encourage you to instead consider the DIX4192 or DIX9211, which do support a 192kHz sampling rate.

    Best,

    Zak