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LMK05318BEVM: Manually changing DPLL settings

david royle
Intellectual 515 points
Part Number: LMK05318BEVM

Run script generates this: (note that the feedback division from 2500MHz to 160KHz is exactly 15625)

 

I need to be able to offset the frequency up to +/-100ppm by manually by writing to the numerator (DCO mode "absolute").

However, the large integer part (3906) makes this range impossible, it needs to be smaller in order for fractional numerator to move it 100ppm.

I modified the feedback as follows:

 

Increasing pre-divider to 16 allows fractional N-divider to have small enough integer part.

Values are chosen to provide exactly the same net division of exactly 15625. 

This works as intended, but my concern is the note in the GUI under step 5:

  • 0
    TI__Genius 12560 points

    Hi David,

    After click on the "Run Script", it will set the all registers mentioned in block diagram. So before run script, it does not change the register manually. As you also able to see the intended output mentioned above.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Intellectual 515 points

    Ajeet,

    I am asking if I can manually manipulate the feedback divider after running the script. I am aware that running the script sets the registers. 

    Dave

  • 0 in reply to david royle
    TI__Genius 12560 points

    Hi David,

    To my understanding, on the fly you can not change (manually) feedback divider after running the script. But I can re-confirm you after checking on EVM with my colleague.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Intellectual 515 points

    Please understand, the TicsPro allows manually modifying the feedback divider after running script, and when I do so in a calculated way it works as intended. The question is there some non-obvious reason that this is not permitted.

  • +1 in reply to david royle
    TI__Expert 8585 points

    Hello David,

    You can modify the feedback divider after a run script, as long as it is done in the correct manner to obtain the correct TDC to VCO relationship. Since you are able to do it correctly and it works as intended, there is no issue with manually setting the feedback divider.

    Regards,

    Kia Rahbar