Thank you Keith,
There was an error in the schematic, the reference is 3V not 3.3V.
The 25 mV offset is relative to 1.5 V reference. It is not possible to connect the 1 mOhm resistor to A_REF, the only way to reduce the common mode voltage would be supplying the Opamp from +-5V.
The datasheet talks about 150 uV/V sensitivity to power supply voltage. Provably the difference between nominal (10 V) and operating voltage is the reason for this offset: (10 V - 5 V)* 150 uV/ = 750 uV
This makes sense... If this is right, my answer changes to:
-Is it normal to specify 150 uV "max input offset voltage" in the datasheet and have an offset drift depending on supply voltage that makes the real max offset 750 uV?
Ernest
---------- Post added at 14:10 ---------- Previous post was at 14:08 ----------
Dear FvM,
Yes 0.1% resistors are assembled, I actually measured their value before mounting them.
Ernest