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LMX2571EVM: Changing spurious level

Mochi
Genius 3885 points
Part Number: LMX2571EVM
Other Parts Discussed in Thread: LMX2571

Hello,

Our customer is evaluating LMX2571 on the EVM then a strange phenomenon is observed. 

Inputted 16.8MHz TCXO and output 900MHz. PLL output is very clean at initial as attached data.

After a while, it is about 4 min, the spurious signal level is increasing.

Then apply initialization, the spurious is go away and repeat same phenomenon after 4min.

Do you see any issue on registers setting or any other concern?

Regards,

Mochizuki

  2571_900.tcs

  • 0
    TI__Guru* 86080 points

    Hi Mochizuki-san,

    I tried this configuration, I don't have the problem.

    Since you are using TCXO, you should not enable the internal termination, this will overload the TCXO.

  • 0 in reply to Noel Fung
    Genius 3885 points

    Hi Noel,

    Thank you very much for your advice.

    We suggested the customer to try to remove internal termination.

    So far no negative update is received.

     

    Regards,

    Mochizuki  

  • 0 in reply to Mochi
    TI__Genius 9250 points

    Hi Mochi,

    Let us know if there is any further help needed.

    Best,

    Asim

  • 0 in reply to Asim Khan
    Genius 3885 points

    Hi Asim and Noel,

    Our customer has reported 36pin OSCin* connection was not correct in this evaluation.
    Diff input mode is configured on IFBUF_SE_DIFF_SEL.
    Because Diff input shows better spurious characteristics than SE input in their previous experiment.
    TCXO output was inputted 34pin OSCin but 36pin OSCin* was left floating with 50ohm termination
    When they connect it to GND then the issue is disappeared.
    So the conclution is 36pin connection was not appropriate in this evaluation.

    Regards,
    Mochizuki