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TLV320AIC3120: MCLK calculation fomula

Hyun woo Kim1
Intellectual 420 points
Part Number: TLV320AIC3120

Dear TI members, 

MCLK should be supplied externally 12.288MHz clocke source to make 48kHz sample rates.  12.288MHz is divided by 256 and get 48kHz 

why 256 is selected to make 48kHz sampling frequency ? is there any particular reason ? 

Best regards, 

  • +1
    TI__Genius 13980 points

    Hi,

    Within audio there are standard (common may be better word) audio frequencies based off commonly used sampling rates. The MCLK frequency is a function of how you configure your digital audio; the function is: Channel count [2:8] * Word length [16:32] * Sampling frequency 

    For example, 2-Ch * 32-bit WL* 48kHz Fs = 3.072 MHz. Your BCLK/MCLK must be >=3.072MHz, this is an MCLK/Fs ratio of 64 (This is the minimum), you could also supply a 128*fs (6.144Mhz), 256*fs (12.288Mhz) MCLK as well. 

    What MCLK you supply is a function of standard audio sample rates (Fs=16Khz, 32kHz, 44.1kHz, 48Khz, 96kHz, etc.), and that is what most datasheets for audio IC's are referencing. However, the user Fs can be any frequency so as long as you provide the necessary clocks to support it.

    When the input MCLK or other source clock is not an integer multiple of the audio processing clocks then using an on-board PLL is necessary.

    What clock frequencies are supported vary by device and whether a PLL is available, more information can be read in below links. As ASI clock configurations change by device you can typically find them linked on the product page on ti.com 

    https://www.ti.com/lit/an/slaa469/slaa469.pdf

    https://www.ti.com/lit/an/slaa716/slaa716.pdf?ts=1674157475339&ref_url=https%253A%252F%252Fwww.google.com%252F

    https://www.ti.com/lit/an/slaa892/slaa892.pdf