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LMK05318B: LMK05318B cannot output 153.6MHz and 491.52MHz at the same time

Allen Lu
Intellectual 2470 points
Part Number: LMK05318B
Other Parts Discussed in Thread: LMK5C33216

Hi team:

 My customer want to set 153.6MHz and 491.52MHz at the same time, but does not work, is there any methods to make it works?

 Use case: 491.52MHz is for AFE ref clk, but since we can not generate 491.52Mhz, we have to decrease to 368.64MHz、122.88MHz ,but it will cause AFE have bad EVM performance.

 perhaps we can make this clk works , and no issue with our AFE. 

  • 0
    TI__Mastermind 29022 points

    Hi Allen ,
    To make sure I understand, PRIREF is 491.52 MHz? Is this SE or differential signal? 
    Following the outputs I see in the image and the statement above saying customer requires a 491.52 MHz output it looks like you require three frequency domains and this device is only capable of covering two frequency domains. 

    Can you please list:
    Input(s) including format type
    Which reference to prioritize

    Output frequencies desired including format type

    Regards, 

    Vicente 

  • 0 in reply to vicente flores prado
    TI__Intellectual 2470 points

    Hi Vicente:

     tks for your reply. but i think i am not familiar with this type device, can you explain the why this 491.52mhz among these frequency belongs to 3 frequency domains?

    here attached the reference clock description range.

    To make this config more clear, i attached the customer config file also:

    lmk05318b_config.zip

  • +1 in reply to Allen Lu
    TI__Mastermind 20900 points

    Hi Allen,

    you do need a VCO frequency which is 2.4576GHz or an integer multiple of that. LMK05318b PLL2 VCO range is 5.5 to 6.25GHz. So, you cannot generate both frequencies at the same time.

    Please have a look at LMK5C33216 instead. This device has a 2.4576GHz BAW based VCO which provides superior performance for your frequency plan.

    regards,

    Julian