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ADS1115: Input impedance of ADS1115

Part Number: ADS1115

i read the datasheet of ADS1115 ,i came across a table that has different ranges of common mode impedance and differential mode impedance ,In my application i am using a FSR of 6.144 for that the common mode impedance is 10Mohm and differential mode impedance is 22Mohm. so how can i calculate the effective input impedance of ADS1115?

  • Darshan,


    I think you've pointed this out before, but the input impedance looks like the following from Figure 26 in the datasheet:

    There is both a differential and common-mode component to the input impedance. The input current (if you look at it that way) will vary with the voltages of both the AINP and AINN inputs and cannot really be decoupled.

    However if you are using the ±6.144V FSR and have the ADC to make single ended measurements (tying AINN to ground), you can approximate the 0.7V discharge point for the common-mode impedance as ground. Then the equivalent impedance appears to be ZDIFF||ZCM.

    Then the input impedance looking into AINP is 10MΩ||22MΩ, which is about 6.9MΩ.


    Joseph Wu

  • thanks Joseph Wu