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TRF3722: TRF3722 CAL_CLK

HENRY JUNG
Expert 2030 points
Part Number: TRF3722

Dears.

In the TRF3722 data sheet CAL recommend 600 Khz.

When using CAL_CLK at 600khz or more, what kind of problem will occur?

What is the problem with using 625khz?

Thank you.

  • 0
    TI__Intellectual 2245 points

    Hi Henry,

    The CAL_CLK is what drives the calibration logic for the device, which is a scaled version of the reference frequency based on CAL_CLK_SEL. Using a faster CAL_CLK frequency, such as 600 KHz,  would result in a faster calibration time, but at the cost of accuracy. What I mean by losing accuracy is that the logic may choose a non-optimum VCO, that would still be locked at the desired frequency but will be on the verge of going out of lock. Small variations in temp, voltage and frequency may push it over the edge. So by having a CAL_CLK over 600 KHz, then the device is more susceptible to this type of problem.

    The recommendation is to keep the CAL_CLK_SEL to something like /16 to /128 to keep the CAL_CLK slow in order to provide the VCO calibration logic more time to choose the optimal VCO.

    If locktime is something of a concern to you, then I recommend checking out the TRF3765 Synthesizer Lock Time appnote for  more information on the digital calibration.

    Regards,

    -Oscar