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LAUNCHXL-F28069M: ADC

user5075334
Prodigy 70 points
Part Number: LAUNCHXL-F28069M
Other Parts Discussed in Thread: BOOSTXL-DRV8301, DRV8301

Hello,

I created a simple model in MATLAB/SIMULINK to analyze the ADC of the F28069M. I plugged a BOOSTXL-DRV8301 into one of the 40-pin connectors and connected a 24V power supply. So there is no motor or anything else connected.

I measure the following current wave:

I wonder about the current peaks in the blue wave.

It doesn't matter which 40-pin connector I plug the DRV8301 into and I've already replaced the F28069M board and the DRV8301 board with new ones.

Does anyone have any idea why there are these peaks in the blue wave?

Yours sincerely

Stephan

  • 0
    TI__Guru* 77390 points
    Stephan,
    Could you list out the settings you are using for the ADC on the MCU? There are some errata on this device regarding the 1st sample of the ADC from an idle state, I want to make sure we are avoiding that as it can give the kind of data you are seeing.

    Best,
    Matthew
  • 0 in reply to MatthewPate
    Prodigy 70 points

    Hello Matthew,

    thank you for your answer. Here are the pictures of my settings:

    Best regards,

    Stephan

  • 0 in reply to user5075334
    TI__Guru* 77390 points
    Stephan,
    While the max clock rate of the F28069 is 90MHz, the max clock rate of the ADC is only 60MHz. If the CPU is running at 90MHz, then you will need to divide SYSCLK by 2 to get under 60MHz(will get 45MHz ADC clock). Please try changing this setting and see of the noise spikes go away.

    I think this is the primary driver of any issue, however, there is also the first sample errata I mentioned. To work around this, please set up SOC1 with exactly the same parameters you have for SOC0. This will cause the ADC to sample the B1 input 2 times, back to back. You will need to use the second result(ADCRESULT1) and discard the 1st(ADCRESULT0).

    You can do the above incrementally or all at once, let me know if this addresses the issue you are seeing and if not we can continue the debug.

    Best,
    Matthew
  • 0 in reply to MatthewPate
    Prodigy 70 points

    Hello Matthew,

    I made a mistake in the screenshots shown above. My settings for the ADC are shown in the following Pictures:

    Sorry for the mistake. 

    But I have changed the settings for the ADC clock, as shown in the following Picture:

    Unfortunately, that didn't change anything.

    Best regards,

    Stephan

  • 0 in reply to user5075334
    TI__Guru* 77390 points

    Stephan,

    Please try changing your ACQPS from 7 to 8.  There is another errata regarding the use of ACQPS = 7, basically the advisement is not to use this value for ACQPS.

    http://www.ti.com/lit/er/sprz342n/sprz342n.pdf   

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Prodigy 70 points

    Hello Matthew,

    I changed ACQPS from 7 to 8, but this didn't help.

    Best regards,

    Stephan

  • 0 in reply to user5075334
    TI__Guru* 77390 points
    Stephan,
    Based on the initial post, since there is no motor connected/running I have been assuming these blue spikes are being caused by the ADC sampling network and debugging that way. Would it be possible to put a scope on the ADC input during the conversions and see if the spikes from the DRV are physically present; that is the ADC is reporting correctly and the system is generating these spikes?

    Another alternative to debug this would be to multi-sample the ADC input each time and see if the blue spikes are present on all samples or just the initial sample. Giving multiple samples would allow the ADC to eventually reach steady state with what is on the pin if this is the issue. If the samples are all the same it would also indicate, like the above, that the noise is coming from the system vs the ADC S/H.

    Best,
    Matthew