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TAS5558: TAS5558 PLL filter circuitry - inconsistency in datasheet and EVM documentation

t0mmy
Prodigy 75 points
Part Number: TAS5558
Other Parts Discussed in Thread: TAS5634, TAS5548

Hi,

I'm working on a schematic with the TAS5558 and 3 TAS5634. Now I'm struggling over the external PLL filter components of the TAS5558:

  • datasheet page 5: VR_ANA - "A 0.1-µF low-ESR capacitor should be connected between this terminal and AVSS_PLL"
  • datasheet page 9: external components typical values: 100n, 10n and 200R
  • datasheet page 112: Recommended External Components show a completely different usage of the pin VR_ANA and PLL filter values. Also here is the TAS5548 shown with crystal resonator instead of MCLK input.

Because every schematic I see (EVM modules, customer image uploads, ...) is like page 112,  I suppose this is the correct way to go?

  • 0
    TI__Mastermind 22120 points
    Hi Tommy,

    Thank you for pointing this out to us. I've been looking into correcting this but for the meantime it has confused a few other people.

    You are correct in your assumptions to follow the EVM module schematic to achieve the best performance!

    Best Regards,
    Robert Clifton
  • 0 in reply to Robert Clifton56
    Prodigy 75 points
    Hi Robert,

    thank you for helping me (and others) on this.

    One more thing I noticed today: The MCLK is misspelled in the pin configuration table. Also the frequency range is 2 .. 50MHz and later (page 12) the document says "The external crystal used must be 12.288 MHz".
    Is there any usecase where you not want to use the 12.288MHz clock?
  • 0 in reply to t0mmy
    TI__Mastermind 22120 points
    Hi Tommy,

    Thanks for catching that typo.

    I think you're getting the MCLK frequency confused with the external crystal frequency. I personally can't think of any use case where you wouldn't want to use 12.288MHz seeing as how we specifically only recommend using 12.288MHz.

    Best Regards,
    Robert Clifton
  • 0 in reply to Robert Clifton56
    Prodigy 75 points

    Hi Robert,

    isn't the external crystal the same as MCLK? Chapter 8.1 says: "The TAS5558 can be driven by an external crystal or an external MCLK."

    But I will continue with a 12.288MHz oscillator.