Do you have the data of the load fluctuation for ADP2120?
eg; 0.2A ---> 1A curent grow up as transient.
I cant find it on your datasheet.
Only found 0A at max output on Fig.24,27, it is the load transient.
load transient depends on the ammount of capacitance added to the output.
You may want to consider using the ADP2120 design tool to identify how much capacitance you will need for a specific transient requirement.
ADP21xx Buck Regulator Design Tool
ADP2105, ADP2106, ADP2107, ADP2108,
ADP2109, ADP2118, ADP2119, ADP2120, ADP2138, ADP2139, ADP2164