The data sheet states the reference output current is 100nA. However on the example circuit (figure 90) REFIO is loaded with two ADA4841-2 inputs each one with 3uA (typ) to 5.3uA (max). Is it safe using this example circuit as is?
The AD9704/AD9705/AD9706/AD9707 are the fourth-generation family in the TxDAC series of high performance, CMOS digital-to-analog converters (DACs). This...
AD9707 on Analog.com
I would follow note 3 under table 1 in the data sheet if using REFIO as a reference for an external amplifier. The note states that you should use a buffer with an input current less than 100nA for this type of application. I would say that figure 90 is a block diagram not a ready to use circuit.