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TMS320F28377D: ADC input impedance

Seven Han
Intellectual 600 points

Part Number: TMS320F28377D

Hi,

Just as the database，can Ron be considered as the ADC input impedance of f28377d or？

thank you。

  • 0
    TI__Guru 60865 points
    Hi Seven,

    The ADC input is high impedance when not sampling. When it is sampling, it is necessary to charge Ch to less than 1 LSBs (usually 0.5LSBs or 0.25 LSBs) of the final value during the S+H time (controlled by the ACQPS setting). Whether this can happen depends on the duration of the S+H, the R and/or C on the pin (Rs is shown in the figures above, but the input capacitance on the pin, Cs, is not shown), and the bandwidth of the driving circuit.

    Usually you would want Rs < 50 ohms, Cs around 10x to 20x Ch, and the driving op-amp to have roughly at least 10MHz of bandwidth.

    There will be an average current in (or out) of the pin that is proportional to Ch times the sample rate.