VDAC offset can be a maximum of 1LSb. This is 4mV in 1V mode and 16mV in 4V mode. In additon, if you are using an Op-Amp to buffer VDAC output, the Op-amp offset(max 1.5mV) will be an addition contribution
1.4 mV is equivalent to 1.4 mA thru 1 ohm. So other factors can be board
layout (trace resistance), split grounds, and where you took your ground
reference, a number of factors, in addition to VDAC specs.
Some additional info that may be of help, attached. AN280 in particular.
All AtoD Error6.zip 12.1 MB