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AFE7900EVM: Reference clock for EVM is unclear

franziskus
Expert 7478 points
Part Number: AFE7900EVM

Tool/software:

Hi,

the AFE79xxEVM_TSW14J58_Bringup.pptx mentions the following:

For coherent sampling a 10MHz reference should be provided to the LMK through SMA J14.

However, the config scripts there is 491.52 or 983 MHz?

Can you tell what is correct?

Best regards

  • +1
    TI__Genius 14961 points

    Hi Franziskus,

    The Bringup Guide is correct and should be followed. On the AFE7900EVM we use a 122.88MHz crystal which is why the reference from the LMK to the AFE is 491.52MHz. 

    For coherent sampling we need to have a common source for the Rx input and LMK clocks, so we input a 10MHz reference and use the LMK PLL1 to lock the 122.88MHz crystal to it.

    In regards to the lmkParams.inputClk parameter in the script, this parameter is not used when the "lmkParams.pllEn" parameter is set to 'False' so a 983.04MHz input is not required. For more information on the script parameters we recommend referencing the "AFE79xx_Configuration_Parameters" Guide in the secure resources folder. 

    Regards,

    David Chaparro