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Original question:

LMX2820: Software Patch that must be inserted when using instant cal

LMX2820: Calibration Failures and Retry Requirements

bob miller
Prodigy 40 points
Part Number: LMX2820


Tool/software:

In step 13 of "LMX2820: Software Patch that must be inserted when using instant cal"  you mentioned that if the calibration fails, start over.  Do you expect the calibration to fail occasionally?  I've placed the Initialization and Calibration into a constant loop.   I'm seeing close to a 1% Calibration failure rate.  The failures tend to cluster in time.  Is this to be expected?  My hardware and the EVB show the same behavior.  

  • 0
    TI__Guru** 109470 points

    Hi Bob,

    If you have the doubler calibration enabled, then yes, there is a very small chance that the calibration will fail. If your application does not need to use the VCO doubler, do not enable doubler calibration. 

  • 0 in reply to Noel Fung
    Prodigy 40 points

    Noel, 

    1.  In our application we use the Doubler

    2.  The DBLR_CAL_EN bit is always disabled.  Is this correct?

    3.  The INSTCAL_DBLR_EN bit is always enabled.  It is turned on during Initialization right after the RESET cmd.  Perhaps this shouldn't be turned on until we enter calibration, ie at the same time as the INSTCAL_EN bit is applied?

  • 0 in reply to bob miller
    TI__Guru** 109470 points

    Hi Bob,

    Since you use InstCal and doubler, setting DBLR_CAL_EN = 0 and INSTCAL_DBLR_EN = 1 is correct.

    A VCO calibration with INSTCAL_DBLR_EN =1 and DBLR_CAL_EN = 0 would not do doubler calibration. It is safe to set INSTCAL_DBLR_EN = 1 during initialization.

    The unlock is purely due to VCO doubler calibration, as long as we do a VCO doubler calibration, no matter if it is an no assist, full assist or InstCal calibration, there is a very small chance the VCO doubler calibration will fail.