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TAD5142: Supported Clock Rates & Output Support

Evan Cornell
Expert 1410 points
Part Number: TAD5142
Other Parts Discussed in Thread: PCM5100A, TPA3251, TAD5112

Tool/software:

Two questions on TAD5142.

1. If operating in slave mode (I assume this is what is meant by target mode), can TAD5142 operate at sampling frequencies off of the normal audio rates? For example, if I feed TAD5142 with FS=104kHz and bitclock=64*104kHz=6.656MHz, will that work properly? I do this now with PCM5100A.

2. Does TI have any recommendation on suitability for TAD5142 directly driving the input of TPA3251 class-D amplifier? Any example schematics? I currently use PCM5100A + 2x op-amps to feed TPA3251, and it would be great to compress that all down to TAD5142.

  • +1
    TI__Mastermind 39395 points

    Hi Evan,

    Since this is a hardware device, you must sample in one of the frequency bands listed below:

    104k isn't available. If you use the software version of the device, TAD5112, you'll be able to set up the device for 104k sampling but you'll need to program the clock settings.

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Expert 1410 points

    Jeff,

    How does that work, since in slave mode, all that TAD5142 is going to know about is the bit clock and frame sync ratio? There's no absolute frequency reference, no MCLK.. is there an internal oscillator or something that determines the absolute frequency value of the input?

    Thanks,
    Evan

  • 0 in reply to Evan Cornell
    TI__Mastermind 39395 points

    Hi Evan,

    There's an internal clock tree to set up the modulators that run the DAC. BCLK is typically the input to this tree and acts as the reference. That's why there's limitations on the sample rate.

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Expert 1410 points

    Jeff,

    Can you give any more details on how this works?

    I just received my TAD5142EVK and did the following test with audio tester (providing I2S clocks & data from tester, reading back differential output):

    1kHz output tone, 0dBFS.

    Over the following frequency ranges, I get ~2Vrms DAC output as expected: 

    • 4-57 kHz
    • 79-116 kHz
    • 157-234 kHz

    But ranges 58-78 kHz and 117-156 kHz, there is no output, despite proper clock ratios (BCLK = 64*FSYNC).

    I would like to understand more clearly why the TAD5142 behaves in this fashion, as my application requires a lot of non-audio sampling rates.

    Thanks!

  • 0 in reply to Evan Cornell
    TI__Mastermind 39395 points

    Hi Evan,

    Are you sweeping through FSYNC frequencies here? In those ranges the internal clock tree may be falling out of its ability to auto configure the internal clock dividers.

    If you need to work with multiple different sampling rates, some of which are non-audio, I highly recommend getting the software version of the device TAD5112. The device is not smart enough to auto configure itself for every frequency in the spectrum, and so some reconfiguration needs to be done. Since the hardware device has no register settings available it won't fit your need here (though it looks like the 104kHz sample rate worked since you say it works between 79kHz to 116kHz?).

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Expert 1410 points

    Jeff,

    I was manually changing the FS on the audio tester serial transmitter. Understood about the recommendation to use TAD5112 for full flexibility.

    We'll stick with PCM5100A for now since it's a known entity and doesn't involve any software work to keep using.. but I appreciate all the feedback on TAD5142.

    Thanks!
    Evan