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AD8210 sourcing current when input are floating

Question asked by Flanbix on Apr 23, 2014
Latest reply on Apr 24, 2014 by Flanbix



There is a behavior I cannot really understand with the AD8210 I am using to sense current.

I seems that when my load power rail is unconnected, the AD8210 is applying voltage to the rail and it is enough to light my "ON" LED.

When the AD8210 has its inputs floating, there are at 4.16V, if I connect my LED to the negative pin, the negative drop at 2.8V and the positive is at 3.6V (LED light up) and with the shunt resistor (150mOhms) both input are at 2.56V (LED light up).

What I was expecting is that when I don't have any current flowing to the current sense resistor because the voltage rail is floating, the LED will be off and the current sense output read 0V. But this is not the case.

Where is my mistake?