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TMS320F28069M: VREFHI pin wiring

Alexis Fetet
Prodigy 20 points
Part Number: TMS320F28069M
Other Parts Discussed in Thread: CONTROLSUITE, LAUNCHXL-F28069M, C2000WARE

Hello,

I am currently experiencing some noise in my ADC readings using Simulink. Simulink allows for External reference for the ADC, and I see that on the documentation (controlSUITE/development_kits/LAUNCHXL-F28069M/HwDevPkg/LAUNCHXL-F28069M_sch.pdf) there is a VREFHI pin, but it does not seem to be connected to anything. Is there any way to use this pin to specify reference voltage? If so, where is it located on the board?

Best regards,

Alexis 

  • 0
    TI__Genius 16570 points

    Hi,

    Unfortunately VREFHI is not available on the LAUNCHXL-F28069M board. Could you give any further details about the noise you are experiencing? It might be possible to address the noise in a different way, as using an external reference on VREFHI would only help with certain kinds of noise. How are your SOCs set up, and what is your effective sampling frequency? 

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 20 points

    Hi,

    In my basic model, I only have 1 ADC on channel A4, set to be on SOC0 with acquisition window of 8 (changed from the default 7). The ADC clock frequency is set to 45MHz and I sample at 1kHz. Changing from 7 to 8 seems to have improved the reading a lot. I still have issues with the long cable sensor, while having no issue with an Arduino.

    Best regards,

    Alexis Fetet

    (short cable sensor)

    (long cable sensor)

  • 0 in reply to Alexis Fetet
    TI__Genius 16570 points

    Hi, 

    In this case, increasing the acquisition window seems like a good idea. Are you able to increase it further?

    I do not think that using an external voltage reference would help in this case, since the ADC is not drawing much current in your setup.

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 20 points

    Hi,

    Unfortunately that does not improve the reading. I tried to raise the priority of the SoC which did not improve the reading either. Slowing the ADC clock did not improve the reading either.

    I have read that other people had similar issues with Simulink and came to the conclusion the issue was coming from Simulink code.

    https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/844717/launchxl-f28027-noise-in-adc-reading-simulink

    I have opened a ticket with MathWorks.

    Best regards,

    Alexis Fetet

  • 0 in reply to Alexis Fetet
    TI__Genius 16570 points

    Hi,

    Are you able to try sampling this channel with an example project in Code Composer Studio? If you download C2000WARE, you could import a starter ADC example from C2000WARE/device_support/f2806x/examples/c28/adc_soc 

    From there, it should be pretty easy to modify the example to sample whichever channel you want to use.

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 20 points

    Hi,

    I successfully ran the GpioToggle and EPwmUpAq examples, but the AdcSoc configuration seems to not accept my f28069m (see capture below).

    Beside, my understanding is that I need to set up an SCI communication to access the results, is that correct?

    Best regards,

    Alexis Fetet 

  • 0 in reply to Alexis Fetet
    TI__Genius 16570 points

    Hi Alex,

    The JTAG connection from your USB cable to the launchpad should be sufficient to load and run the program, and you can watch the results by right clicking on a variable and selecting "add watch expression". This will make the variable show up in the window in the top-right side of your CCS. 

    Could you please select View > Target Configurations? Then please open the projects dropdown menu and find the target configuration. Could you then please right-click and select launch target configuration? Then could you take a screenshot of your debug menu and post that here? 

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 20 points

    Hi,

    The debug configuration was using the default configuration. After manually specifying the path to the .ccxml file, I managed to get it working.

    Here are the values I get (I extended the array to 50 elements and increased SOC to 8), and I can see the same noise (samples 14 and 16). I believe the issues is then more related to my setup.

    Best regards,

    Alexis Fetet

      
    Voltage1    [50]    [834,835,834,832,828...]    0x0000A100@Data
    [0]     834
    [1]     835
    [2]     834
    [3]     832
    [4]     828
    [5]     821
    [6]     832
    [7]     832
    [8]     833
    [9]     836
    [10]    819
    [11]    835
    [12]    837
    [13]    834
    [14]    804
    [15]    834
    [16]    861
    [17]    841
    [18]    836
    [19]    834
    [20]    833
    [21]    833
    [22]    835
    [23]    833
    [24]    834
    [25]    833
    [26]    833
    [27]    833
    [28]    834
    [29]    832
    [30]    835
    [31]    836
    [32]    835
    [33]    836
    [34]    834
    [35]    833
    [36]    830
    [37]    833
    [38]    832
    [39]    833    
    [40]    837
    [41]    833
    [42]    837    
    [43]    831    
    [44]    833    
    [45]    834    
    [46]    832    
    [47]    831
    [48]    833    
    [49]    840
  • 0 in reply to Alexis Fetet
    TI__Genius 16570 points

    Hi,

    Yes, it seems likely that the noise is related to your setup. Here is a resource that may be helpful in diagnosing your issue: https://www.ti.com/lit/slyy192

    Please let me know if you have any more questions.

    Best Regards,

    Ben Collier