capacitive load is acceptable?
The settling time plots in the datasheet are all done with a 100pF load, and
the part is very stable with this much capacitance or less. According to our
Engineers AD8221 could probably drive about a nanofarad before going unstable
(note this has not been tested in lab).
To drive a larger capacitive load, one small resistor is recommended between
the AD8221 and the capacitor. Best way to determine the correct resistor value
is empirically using a square wave input into the AD8221 and adjusting the
resistance until the square wave looks reasonable at the output.
(There is a note on driving a cable on page 21 of AD8222 datasheet (dual of
AD8221),you may also find this useful).