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CDCM6208: Crystal stability and tolerance requirement

Madhu Sharma
Expert 2915 points
Part Number: CDCM6208


Hi,

I am using CDCM6208V1 in Pin mode ( Pin mode 19). Also I am planning to use SEC_REF as the input. 

Please let me know what must be the stability and tolerance requirement for the crystal to be connected to SEC_REF.

Regards,

Madhu.

  • 0
    TI__Expert 8865 points
    Hi Madhu

    The XTals with 7pF load capacitance and <200uW drive level are preferred. Please refer to the section "7.11 Crystal Input Characteristics" of the datasheet for more information.

    Best regards
    Puneet
  • 0 in reply to Puneet Sareen
    Expert 2915 points

    Hi Puneeth,

    Thanks for the reply.

    section "7.11 Crystal Input Characteristics" of the datasheet doesn't specify anything about crystal stability & tolerance.

    As you mentioned, other factors like capacitance and drive levels are mentioned in that section.

    So please let me know what must be the stability & tolerance for the crystals.

    Regards,

    Madhu

  • 0 in reply to Madhu Sharma
    TI__Expert 8865 points
    Hi Madhu

    Frequency stability and tolerance depends on the allowable frequency deviation in your application. Typical xtals specs are 20-30ppm, but you can also have more expansive xtals with tighter specs.

    Best regards
    Puneet
  • 0 in reply to Puneet Sareen
    Expert 2915 points
    Hi Puneeth,

    Thanks for the reply.

    Can you please let me know how the output frequency deviation is related to crystal stability?

    Regards,
    Madhu
  • 0 in reply to Madhu Sharma
    TI__Expert 8865 points
    Hi Madhu

    Xtal manufacturer generally specifies the frequency tolerance at room temp and the frequency stability over temperature.
    The first one refers to the part to part frequency tolerance measured at room temperature. The second one refers to the frequency deviation over temperature.
    For instance, if a requirement is for 100 ppm maximum total allowable frequency deviation over the temperature range of 0° to 70°C, you should use a crystal that has 50 ppm tolerance at room temperature (25°C) and 50 ppm stability over the operating temperature.

    Best regards
    Puneet