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TMS570LC4357: Effects of Discharge Prescaler and Sample Window on ADC Accuracy

Kevin Peterson
Prodigy 100 points
Part Number: TMS570LC4357

Hello,

I was wondering if anyone has any analysis or insight about how much the discharge prescaler and sample window setting impact the overall accuracy of the ADC. I'm just trying to get a better idea of how fast I can run the ADC and what level of accuracy I may be sacrificing by doing so.

Currently I have the discharge prescaler set to 1U and the sample window at 6U (which I believe is the minimum, according to the datasheet--this puts my total sample time at 0.651 us). I'm sampling 25 inputs in ADC2 Group 1 continuously at an ADCLK of 37.5MHz with 12 bit resolution.

Thanks,

Kevin

  • 0
    TI__Mastermind 49120 points

    Hi Kevin,

    The sample capacitor discharge mode does not help in reducing the sampling time required unless the next channel to be converted has a level close to ground. The actual sample time required for the charge on the sampling capacitor to settle within 2 counts of the external input is dictated by the external source impedance characteristics. Please refer to this application note for more information: http://www.ti.com/lit/an/spna118b/spna118b.pdf

    Also, consider using multiple conversion groups within the ADC module to over-sample the 25 inputs . Refer to this post for an example:

    Regards, Sunil