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Using the AD22105 as a cooling setpoint detector

Question asked by subtractor on Dec 21, 2017
Latest reply on Jan 30, 2018 by KarenNE

I am planning to use the AD22105 as a replacement for the obsolete DS1821 sesor. In my design it operates as a standalone thermostat in reverse polarity as shown on figure:

Output graph DS1821 in reverse polariy thermostat mode

In datasheet for the AD22105 it is mentioned that “AD22105 can be used to detect transitions from higher temperatures to lower temperatures by programming the setpoint temperature 4°C greater than the desired trip point temperature. <...> In this mode, the logic state of the output will indicate a HIGH for under temperature conditions.”. Still this is unclear to me how this works. How would the sensor figure out that I want to put it in this mode and not to just set the setpoint temperature somewhat higher?

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