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SM73201-ARC-EV: External ADC

Devinda Molligoda
Intellectual 380 points
Part Number: SM73201-ARC-EV
Other Parts Discussed in Thread: TMS320F28033, SM73201

Hi,
The TI RD-195 DC arc detection evaluation board uses a 16bit external ADC. Is it because the internal 12bit ADC of the TMS320F28033 is having less resolution, or is there any other reason.

Regards,

Devinda

  • 0
    TI__Genius 14270 points
    Hi Devinda,

    The external ADC has much higher SFDR (Spurious Free Dynamic Range), which is needed to handle high interferring signals. If the ADC does not have sufficient SFDR, then the ADC may add noise to the sampling which degrades the sensing performance.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Intellectual 380 points

    Hi Chris,

    Thanks for your reply. 

    Could you also please tell me why a 40-100kHz bandpass filter is used in front of the ADC? 

    If the board is intended to be used in solar inverter application there is a high chance that the switching frequency will fall in this band. Is there a particular reason for selecting this range?

    Alternatively can I pull the bitstream out of the SM73201 ADC and do the filter operation in the DSP without having the analog filter part?

     

    Regards,

    Devinda.

  • 0 in reply to Devinda Molligoda
    Intellectual 380 points
    Adding to this, in the DSP code, the 40 to 100kHz band is devided into 2 bands and the lower band is given more weight (4x) in detecting the ARC. Do you have a reference for this claim or was it verified statistically?
    Thanks!

    Regards,
    Devinda
  • 0 in reply to Devinda Molligoda
    TI__Genius 14270 points
    Hi Devinda,

    It is critical to remove components above 120kHz, as they will alias into the conversion results. The low-pass components are used for implementations which do not use a CT to provide isolation - removing line frequency and harmonics is critical.

    Even with the high SFDR of the SM73201, without filtering it is possible to clip the input, as the SM73201 has a BW > 3MHz.

    The included algorthim of the RD-195 is highly effective for filtering in-band switching components.

    Regards,

    ChrisO