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ADS8588H: input impedance mismatch

justifice zhou
Intellectual 400 points
Part Number: ADS8588H

Hi,

in the datasheet it's said "In order to maintain the dc accuracy of the system, matching the external source impedance on the AIN_nP input pin with an equivalent resistance on the AIN_nGND pin is recommended"

I wonder how to calculate the error if the input resistance is not matched?

  • 0
    TI__Mastermind 37955 points

    Hi justifice,

    The intertnal common-mode voltage is set by the internal voltage reference and the feedback loop. If the impedance on the negative input does not match the impedance on the positive input, the common-mode voltage will deviate from the expected know value and it will produce an offset error. It's not easy for you to calculate it without knowing the value of internal components. The error is small and it can be neglected in most designs, but the matching impedance is always recommended for a precise design. 

    Regards,

    Dale