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ADC081 application problem ?

Hi Sir

We have a slight problem with ADC081. When the Analog in pin is floating (not connected) the readings from "conversion result register" are erratic.

The expected value should be 0, or an indication of floating.

 

How can we detect if there is voltage present on the analog pin?

                                                     Bogey

  • Hi Bogey,

    If the analog input pin is floating, the voltage on VIN pin is indeterminate. This pin has diodes to VA and GND for ESD protection (Figure 22 in data-sheet). Depending on the leakage, the pin may tend to ground or positive rail over a period of time.

    Hence, it is not possible to expect a particular code from the ADC when VIN is floating.

    You could set the upper and lower thresholds of the ADC to detect the presence of a voltage beyond the programmed thresholds. However, with VIN floating, this feature may lead to false ALERTs.

    I would recommend biasing the input pin to a known voltage. You could then set the thresholds around this known voltage.

    Regards,
    Rahul