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RM57 ADC Self-Test

Dmitri Zakharevski59
Intellectual 905 points

Hello,


I am testing the ADC Self-Test Code I have written and have a quick question about the results I am getting.

I am testing all 41 pins available to me on the RM57 and expect them to be in the "Open" Condition as derived from Table 22-4 in the RM57 Technical Reference.

From reading other posts about the ADC self test, I expect ADreflo to be 0x0 and ADrefhi to be 0xFFF, how ever I do not always receive that result.

ADrefhi is consistently reading 0xFFF but it looks like ADreflo will mostly read 0x0 as expected, but has a range from 0x4-0x0 that I have seen.

The ADreflo results fluctuate on subsequent re-runs of the test.       

Sample results:

Vn 3300

Vd 4

Vu 4095


Vn 3326

Vd 0

Vu 4095


Is this expected behaviour for Open pin condition? It does not say "Approximately" in the datasheet.

Do you recommend a <10 check for ADReflo? or something along those lines?

Thanks!

  • 0
    TI__Guru 72500 points
    Two things may be causing the higher readings of ADREFLO. Perhaps the sample time is insufficient to discharge the internal capacitance and the capacitance of the open pin. Try increasing the sample time. Also, if there is noise on ADREF, then there will be some error induced.
  • 0 in reply to Bob Crosby
    Intellectual 905 points

    Bob Crosby said:
    Two things may be causing the higher readings of ADREFLO. Perhaps the sample time is insufficient to discharge the internal capacitance and the capacitance of the open pin. Try increasing the sample time. Also, if there is noise on ADREF, then there will be some error induced.

    I still have the readings under 10 [0-10] for ADreflo.

    I have used the following settings maximizing wait time before performing the reads:

        adcREG1->CLOCKCR = 0x1F;
        adcREG2->CLOCKCR = 0x1F;

        adcREG1->EVSAMP = 0xFFF;
        adcREG2->EVSAMP = 0xFFF;

        adcREG1->G1SAMP = 0xFFF;
        adcREG2->G1SAMP = 0xFFF;

        adcREG1->G2SAMP = 0xFFF;
        adcREG2->G2SAMP = 0xFFF;

        adcREG1->EVSAMPDISEN = 0xFF;
        adcREG2->EVSAMPDISEN = 0xFF;

        adcREG1->G1SAMPDISEN = 0xFF;
        adcREG2->G1SAMPDISEN = 0xFF;

        adcREG1->G2SAMPDISEN = 0xFF;
        adcREG2->G2SAMPDISEN = 0xFF;

  • 0 in reply to Bob Crosby
    Intellectual 905 points

    ADrefhi Is consistently staying 0xFFF, I have ran the self test code on a Custom PCB as well as the RM57 HDK with the same results.

    I am testing all 41 pins available at once using both ADC1 and ADC2 if it makes a difference. The test did not specify converting each pin vs all pins.


    I can post my code if it would help diagnose the issue.

  • 0 in reply to Dmitri Zakharevski59
    Intellectual 905 points

    One additional Question for self-test. Is there a sequencing requirement that is Missing from the Technical Reference? Can Self-Test be performed after Calibration or does it need to be performed before?

    I am performing self test after calibration of pins if it makes a difference. Does self-test effect the Calibration values at all as well? Should Calibration be re-run after self-test?

  • 0 in reply to Dmitri Zakharevski59
    Intellectual 905 points

    Order of operations is not an issue:

    Are these results still being looked into? Is it acceptable to just check Approximate ADreflo if(Vd < 10)

  • 0 in reply to Dmitri Zakharevski59
    TI__Guru 72500 points
    Since it is not sample time, it must be noise. Using Vd<10 is acceptable for the self test as it is looking for an open or shorted pin.