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PCM1808: PWM instead Crystal with Crystal Driver

Ray Vincent Aranzaso
Mastermind 18180 points
Part Number: PCM1808

Hi,

Customer evaluating PCM1808 on his project.

He uses another codec for his evaluation which takes a crystal input directly but PCM1808 needs a crystal driver separately.

He also have a PWM pin from his SoC that can he use, can he use that PWM on PCM1808 instead of crystal plus the crystal driver?

I hope you can help our customer with his query. Thank you very much.

Best Regards,

Ray Vincent

  • 0
    TI__Mastermind 23050 points

    HI Ray,

    This ultimately depends on the quality of the PWM signal. PCM1808 requires a 40%-60% duty cycle system clock. Typically I don't think PWM SoC signals will be as good as a quality crystal, but if the quality of the signal satisfies the timing requires of PCM1808 then it should work fine.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    TI__Mastermind 18180 points

    Hi Zak,

    Good Day. Please see below for another query of our customer. Thanks.

    One ADC question for PCM1808 about using PWM instead of a crystal, where the latter (crystal) is more reliable: Would increasing the Fs to 384 from 256 alleviate enough of the quality issue? Eg: option (1) is running PWM in 384 Fs mode (2) is running Crystal in 256 Fs mode.
    The reason we ask, is that if the PWM option works then we’ll have the flexibility of changing the sampling rate dynamically in software rather than hardware.

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Mastermind 23050 points

    Hi Ray,

    A higher frequency clock is going to require tighter tolerances so I don't see how this would help them. They need to determine what kind of tolerance the PWM clock has and make sure they can handle any drift that might occur.

    Best,

    Zak