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PCM5121: Selecting desired sampling frequency

Ernest Yong
Expert 4315 points
Part Number: PCM5121

Hi Team,,

My customer is currently looking at using TI Audio DAC for their project.

They are currently looking at PCM5121. Please see the below enquiry:

Pin 14 can be use to choose between I2S Master or I2S slave, and pin 24 can be used to select the audio format

To choose the appropriate sampling rate, do they supply different frequency to SCK to get the desired sampling rate?

The specification state that in hardware mode the SCK Rate is 128 ~ 3072 fs while the BCK rate is 64, 48 ,or 32 fs

How could they actually select the desired sampling frequency?

 

For example, when they supply 24.576MHz to SCK,

There are possibilities of sampling frequencies of

192KHz @ 128FS

96KHz @ 256FS

48KHZ @ 512FS

Etc.

 

In this case, how can they choose the desired frequency?

Thank you.

Best Regards,

Ernest

  • 0
    TI__Mastermind 22170 points

    Hi Ernest,

    There is a relationship b/w BCK and Fs that has to be matched and those coefficients that usually you see are coming from there. Consider the following equation

    BCK=  #of channels x Channel depth x Fs

    So for example if you have a 2channel and 32bit data then BCK=64Fs. So now you can see if you have a sampling rate of 48K, then your BCK has to be   96*48k=3.02MHz.

    On the other hand you can chose your SCK to be a multiple of fs (sck=n*fs) and n is a number that you can select as long as it is 128,256,512 and etc.

    PCM5121 can take maximum SCK of 50MHz ( because min System clock pulse cycle time is mentioned to be 20ns). So you can feed a SCK with the following 2 constraints:

    1) SCK  has to be less than 50MHz and

    2) SCK has to be a valid multiple of your sampling freq that is according to Table 32. System Master Clock Inputs for Audio Related Clocks. So according to this table, if your  Fs is 48KHz, you have 7 choices for sck, whereas if your fs is 384KHz, then you have only 2 choices for sck.

    Kind Regards,

    Arash