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LMX2594: Condition for PLL Unlock

Sadanori Kato
Guru 36540 points
Part Number: LMX2594

Hi,

When the registers were set while the reference signal wasn't input to the LMX2594 and the registers were set again after the reference signal was input, the symptom occurred that PLL doesn't lock.
The interval between setting when the reference signal isn't input and resetting when the reference signal is input is about 10 ms.
So, is there a possibility that LMX2594 will not be locked under the above conditions?

Please let me know if you would need the register setting for LMX2594. I can share it with you via a private message. So, could you please accept my friendship request?

Best regards,
Kato

  • 0
    TI__Genius 11900 points

    Hello Kato-san,

    Please follow this procedure if OSCin is available after registers are set:

    1. Set all registers
    2. OSCin available
    3. After the reference is available write FCAL_EN=1.

    Let me know if this locks the device.

    Thanks,

    Vibhu

  • 0 in reply to Vibhu Vanjari
    Guru 36540 points

    Hi Vibhu-san,

    Thank you for the information.

    I informed our customer of that information and he confirmed that PLL could lock.
    Then, I would like to discuss the first question with you.
    When the registers were set while the reference signal wasn't input to the LMX2594 and the registers were set again after the reference signal was input, the symptom occurred that PLL doesn't lock.
    So, he found that that unlock issue doesn't occur by not writing the registers when the reference clock isn't input to OSCin. Could you please tell me that reason why PLL cannot lock when applying the first procedure to LMX2594?

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru** 107520 points

    Hi Kato-san,

    Calibration requires a valid reference clock to be successful. If there isn't a valid reference clock during calibration, the logic state of some internal blocks will stuck (or hang-up). Even if you attempt to program all registers again, these blocks may not response to the new programming instruction. A RESET is required to get it out from the freeze state.

    In your example, if the first calibration is without a valid reference clock, then before the second full registers write, program R0 with RESET=1. You should be able to get it locked after the second write.

  • 0 in reply to Noel Fung
    Guru 36540 points

    Hi Noel-san,

    Thank you for the detailed information.

    I understand and will contact you if I get additional questions from our customer.

    Best regards,
    Kato