In the AD7656 Eval board design I have, the Vref is buffered by the AD8031.
And this is what I have used in a few years ago design of mine.
No we are opening this design for a new project, and the engineer responsible, told me
he looked and saw the AD8031 has quite high input offset, and it doesn't seem like the best option
for this task.
Can you suggest a better option for the 2.5V buffer at the AD7656 REF_IN_OUT pin?
Best if it will be in a very small case close to the 5 pins SOT-23 package (AD8031ATR) I have used...
You may check the AD8605 if it fits your latest application. Please refer link for the AD8605 datasheet.