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TMS320F28034: ADC Calibration, Correction Factor

abe mathew
Prodigy 180 points

Part Number: TMS320F28034

Section 8.10.2 of SPRUI10 talks about the Procedure to use for ADC Zero Offset calibration.  The procedure calls for setting an artificial offset (value of 80) and then taking an average to account for board noise.  This value is then subtracted from 80.  The resulting "Correction value" is then written into the AdcRegs.ADCOFFTRIM.bit.OFFTRIM Register value.  

My questions are the following:

1.  What is the tolerance on the correction value and what is an acceptable range?  I need to set a warning if the average is outside a threshold +/- tolerance. 

2.  Is there a way to induce a fault for software verification tests by affecting the correction value to push outside its acceptable range?

Appreciate any help that can be provided.

  • 0
    TI__Guru 62975 points

    abe mathew said:
    1.  What is the tolerance on the correction value and what is an acceptable range?  I need to set a warning if the average is outside a threshold +/- tolerance.

    We have no official threshold or tolerance to recommend.

    Personally, I would expect the self-offset trim on your system to correlate with the offset trim that is populated by Device_cal so you could use a handful of devices to determine a rough threshold. However, TI may occasionally change the manufacturing offset trim algorithm so it would be a good idea to use a loose tolerance.  For example, +/- 20 LSB.

    If you have a well-regulated reference voltage of some sort on the board and a free ADC channel, it would probably be more reliable to sample the reference voltage for sanity check.

    abe mathew said:
    2.  Is there a way to induce a fault for software verification tests by affecting the correction value to push outside its acceptable range?

    Can you provide an example? Would it be sufficient to add a value to the OFFTRIM register so that the conversions are wrong?

  • 0 in reply to tlee
    TI__Guru 62975 points
    Abe,

    It has been a while since your last update. I assume that you were able to resolve your issue.

    If not, please reply to this thread. If the thread has locked due to timeout, please create a new thread describing the current status of your issue.

    -Tommy