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TMS320F28377D: Abonormal peak in the sampling of DSP

qianqiang
Prodigy 10 points

Part Number: TMS320F28377D

Hi

    When I was using the ADC of thee DSP, the digital result exhibits a large peak, not regularly. 

    If I tried to enlarge the S/H value in the configuration of the ADC resigister, things turns worse. The best sampling performance is shown as the following figure. Is there any possible reason for this phenomenon?

    The phase-to-phase voltage is sampled by an isolate transformer. I have talso ried to use the differential routing to sampling the phase-to-phase voltage, the amplifier is aslo replaced by higher CMR>80dB. The RC fitler at the output of the OA is 100ohm and 1nF, and the RC filter at the input of the ADC is 10ohm and 10nF.

                            

  • 0
    TI__Mastermind 36526 points

    Hi,

    It looks like this problem is not occurring on your blue and red signals in your graph. Is there any difference in the software for sampling these two signals? 

    As for the filtering, this app note may be useful: https://www.ti.com/lit/SPRACT6

    Best Regards,

    Ben Collier

  • 0 in reply to Benjamin Collier
    Prodigy 10 points

    Hi，

    Thanks for youre valuable comments.

    This phenomenon occurs on the three phase-phase voltage, not limited to the given figures. Things turn very bad if the S/H value increase. I have use the minimized S.H time to get the above figures. 

    I am sorry that the aboved figures are tested on the DSP 28379, not on the DSP28377D.   I have replaced the DSP 28379 into DSP 28377d, the performance of the ADC turns better. But when I increase the phase-phase voltage from 380VAC to 600VAC, the above phenomenon stlll occurs. I am going to check the conditioned circuit again to avoid any interference. 

    But I am still wondering whether the DSP type will affect the performance of the AD sampling?  And, whterter the S/H time slices will affect similarly?

     Thanks

    Qain

  • 0 in reply to qianqiang
    TI__Mastermind 36526 points

    Hi Qain,

    Could you please provide more details about your setup? How are you stepping the voltages down for the ADC? Could you please share your ADC settings? 

    Best Regards,

    Ben Collier