Compliance of 100uA source

I am trying to compare an external resistance value using the constant current source option for comparators to establish
the voltage.

The data sheet for SLG46533 suggests the constant current is sourced from 1.8v (and says input has to be less than 1.8v)
but I still don't know the compliance of the source.

the data sheet for SLG46880 and SLG46826 omits the current source which is available optionally on cmp0 in comparator or pin schematic

the data sheet for the SLG46620 has a the source in the schematic doesn't indicate where the current comes from.

Obviously I need the compliance to figure out the maximum resistance value I can compare with this method. The tolerance
on the current source would be helpful too...

thanks.