I'm having trouble with a AD628 amplifier.
I have to measure a voltage between 0V and 36V using a divider bridge (see picture attached).
The AD628 power supplies are +/-5V.
With a common mode voltage between 0V and 5V, the results are very good (1mV precision).
But when the input signal has a negative common mode voltage between -5V and 0V, the AD628 doesn't allow a differential input voltage less than -0,7-Vcm (for instance : 4,3V for a -5V common mode voltage)
Question: Is there an internal protection connected to the negative rail on the inputs ?