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AD8210 - Vs bleeding thru differential inputs?

Question asked by cocus on May 26, 2018
Latest reply on May 31, 2018 by krisf


I'm trying to use the AD8210 to measure currents in the high-side of a simple BJT regulated power supply.

I saw that after started using the AD8210 for the current control, the output voltage of my power supply didn't go to 0 anymore.

I narrowed the problem to the AD8210 itself, so I got more of those and tried them separatedly

If I only apply 5V to Vs of them, without ANY shunt resistor, nor output load, nor bypass cap, I got around 4.1V in each differential inputs. The same is true if I connect the proper shunt (with no current nor voltage applied to any pin of the shunt).

If I try to ground either input pin with an ammeter, I got almost 5mA that comes from the AD8210 itself. 

Why this is happening? I didn't saw anything related to this in the datasheet, and I expected that both differential inputs to behave like a small load (to ground) ONLY when some kind of common-mode voltage was applied externally.

I'm missing something? Should I use another part?