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LMH0346　- Crystal Parameter

Kawai
Guru 19785 points
Other Parts Discussed in Thread: LMH0346

Hi Team,

Please let me ask you about the recommended crystal parameter.

I believe that below parameter is the specification for the crystal itself.

When implementing to the crystal oscillator circuit (matching), there will be difference in the total frequency tolerance or stability.

What is the target value  for the crystal oscillator parameter which must be followed ?

Our customer will use a crystal which has frequency stability of +/- 30ppm for -10C to +85C.
However, after matching in the circuit (optimization), frequency stability became -98ppm and drive level was 120uW.

Would you have any problem using in this condition ?

Best Regards,
Kawai

  • 0
    TI__Expert 3175 points

    Hi Kawai,

    In general, the crystal parameters are dependent on the particular crystal from your supplier.

    There is some adjustment you should do to bring the crystal frequency to the center (ie 0ppm). Adjustment of the load capacitor will help.

    I will ask the AE of the LMH0346 to follow up on this case.

    Regards,

    TK Chin

  • 0 in reply to T.K. Chin
    TI__Guru* 93670 points

    Hi Kawai-San,

    Our data sheet recommendation was based on a particular Crystal from a Company called Abracon. We have worked with and recommend a crystal from another company called KDS Daishinku. Based on KDS recommendations we should use 15pF loading Cap for their crystal and this meets their drive level(260uW max). The KDS crystal part number is: KDS’s P/N: 1B427000ZZ0A

    Based on testing we did with KDS this resulted in 93ppm frequency tolerance and we did not observe a problem. I suggest if your customer contacts KDS to inquire about this crystal and their recommended settings.

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Guru 19785 points

    Hi Nasser-san,

    Thank you for the information. I had KDS crystal information in the other thread.
    Our customer had been talking with KDS, had a recommended setting result of several frequency tolerance depending on the load capacitance of the crystal.

    I have asked customer to use the crystal with the higher load capacitance which  has better frequency tolerance characteristic, recommended lower value than your test data 93ppm.

    I have one more question.
    What happens when the reference clock 27MHz has larger tolerance or center frequency is drifted to a few hundreds of ppm ? Would output jitter characteristic get worse ?

    Thanks and Best Regards,
    Kawai

  • 0 in reply to Kawai
    TI__Guru* 93670 points

    Hi Kawai-San,

    It depends on the type or architecture of the PLL. For LMH0346 we have not tested with a wider ppm tolerance than specified in the data sheet and operated the device over supply, voltage and temperature. But in general, i would expect the jitter to increase.

    Regards,,nasser

  • 0 in reply to Nasser Mohammadi
    Guru 19785 points

    Hi Nasser-san,

    I understand, thank you very much.

    Best Regards,
    Kawai