In my previous email i was actually talking about a ADC converter.
In the DAC converts the digital input in converted to a current and then its up to the external opamp circuit to convert this current to a voltage.
Page 9 and 10 of the datasheet has two output circuit, unipolar and bipolar and for each one the input/output table.
In these tables there is a -Vref and Vref, I'm not sure but i assume that if your Vref pin is connected to -5v then in these tables
-Vref = -(-5v) which is 5v
and Vref= -5v
Alex