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IWR6843: Required drive level for the crystal

Kei
Intellectual 760 points
Part Number: IWR6843


Tool/software:

Hello,

I have a question about the drive level specified in the crystal section of the IWR6843 datasheet. Could you please explain the principle behind how that maximum value is determined?

Regards,
Kei

  • 0
    TI__Genius 9870 points

    Hi Kei,

    The maximum drive level specification for XTAL selection is derived from the maximum power that the mmWave device can drive the XTAL. Hence, it is recommended to have a XTAL part with greater drive level than 200uW to prevent any wreckage of XTAL.

    Regards

    Ankit

  • 0 in reply to Ankit Mohanty
    Intellectual 760 points

    Hi Ankit,

    Thank you for your answer.
    I suppose the drive level value is determined not only by the mmWave device itself, but also by the entire oscillation circuit (including the crystal itself and peripheral capacitors). Could you please provide more details about the background that led to the specification of a maximum value of 200 µW?

    Regards,
    Kei

  • +1 in reply to Kei
    TI__Genius 9870 points

    Hi Kei,

    The value of 200uW drive level was determined after validation of the XTAL circuit. TI recommends using 4.7uF shunt capacitors and XTAL with load capacitance specification varying between 5pF to 12pF considering the trace parasitic will have a capacitance between 2.6pF to 9.65pF. Various XTAL with lower drive strength than 200uW drive level were tested and found that it will reduce the lifetime due wreckage of XTAL. If the drive level is too high, it will lead to reduced lifetime, accelerated aging, and unwanted harmonics and spurs. Drive level (DL) is the amount of power dissipated in a crystal as calculated in below equation.

    Regards

    Ankit