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ADS1115: Buffer-less measurement

Bumblebee
Expert 2575 points
Part Number: ADS1115

I'm planning to use this chip to measure 4 thermistors (NTC) simultaneously. With a voltage divider config, can I directly attach the thermistors to the inputs of this chip? Are there repercussions if I don't use a voltage buffer for each channel?



  • 0
    TI__Guru* 97465 points

    Bumblebee,



    The input for the ADS1115 uses a switched cap for sampling the input voltage. Because of this, the input appears as an input impedance with differential and common-mode components. From the inputs, it appears like this as a schematic:



    These impedances depend on the FSR range. They are listed in the Electrical Characteristics table here:



    If you are measuring a thermistor, it is likely going to be fine without a buffer. You may get some amount of error because there is some input impedance. It's likely that this error would be very small but it depends on the resistance of the thermistor.

    Do you have a schematic to review?



    Joseph Wu