When drawing a load current at either rail, the output voltage headroom with respect to that rail is limited by the 25 Ω typical channel resistance of the DAC channel

Hi LCJ603 ,

Your computations are correct. However, in the AD5593R Datasheet, under the DAC performance specifications, 25mA is already the short-circuit current in typical conditions.
You may also check Figure 26 for the DAC Output Sink and Source Capability. 
May we know your target application so we can further assist you?

Regards,
Flynn

Hi LCJ603 ,

Your computations are correct. However, in the AD5593R Datasheet, under the DAC performance specifications, 25mA is already the short-circuit current in typical conditions.
You may also check Figure 26 for the DAC Output Sink and Source Capability. 
May we know your target application so we can further assist you?

Regards,
Flynn

I need drive 120ohm resistor ,and supply 20ma max