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TMS320F28335: ADC acquisition, not all channels work as expected

mike buba
Intellectual 470 points

Part Number: TMS320F28335

Hi All,

I was checking ADC channels and acquisition on my TI C2000 F28335 docking station using Matlab Simulink as a programming tool. The power supply is via USB cable.

But somehow, it seems that not all channels behave the same or work properly.  I have plotted outputs:

  • Nothing is connected to the TI card pins (A0-A7 and B0-B7)

  • 1,5 Vdc is connected to the TI card pins (A0-A7 and B0-B7)

Channels A6, A7, B6 and B7 have huge spikes in waveforms > 20 bits. For others, it is +/- 2 bits. 

Is this something to do with the card, or Simulink? A know issue? btw. when I put AC waveform, all changes are OK.

The docking station is R3 and F28335 is 2.2.

Thank You

  • 0
    TI__Guru 62975 points

    Mike,

    I see from the R2.2 schematics that all of the ADC channels have noise-filtering capacitors and ESD protection installed except for ADC-A6/A7/B6/B7.  I suspect that A6/A7/B6/B7 are left free of these components so that users can evaluate the native performance of the ADC without the bandwidth-limiting effects of the filtering capacitors.

    I think that this is the most likely explanation for the behavior that you are seeing.  If this is the case, you should see the spikes attenuate as ACQ_PS is increased.

    -Tommy