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ADS7844: Maximum Source Impedance

Jacob Wyrick
Expert 8655 points

Part Number: ADS7844

Hi team,

My customer is looking to work with the ADS7844 and are curious if there is an maximum source impedance. Do we have a maximum source impedance spec for the ADS7844?

I found a similar question in another E2E forum post, but the link it references - copied below - is dead.

https://e2e.ti.com/support/data_converters/precision_data_converters/int-precision_data_converters/f/75/t/36739.aspx#128302

Thanks,

Jacob

  • +1
    TI__Guru 64805 points

    Hi Jacob,

    Higher source impedances will have a few effects.  First, it will contribute noise which depending on the integrated noise-bandwidth may dominate over the ADC noise-floor.  Second, higher impedances will start to struggle, and then eventually be unable, to charge the internal CDAC sampling capacitor to the proper levels within the acquisition periods.  There will also be some DC errors due to leakage currents into the inputs, outside of the transient charge requirements for the sampling cap.

    For detailed information on #2, which is likely the most important, see this training video.  The slides are available below the video (in pdf form) if you don't want to watch the video:  https://training.ti.com/ti-precision-labs-driving-sar-without-amplifiers

  • 0 in reply to Collin Wells
    TI__Expert 8655 points

    Thanks Collin. It sounds like the general guidance for the input of the ADS7844 is to keep the source impedance as minimal as possible.

    Thanks,

    Jacob