As for all switching power supplies, the layout is an important step in the design. Care must be taken in board layout to get the specified performance.
It is critical to provide a low inductance, impedance ground path. Therefore, use wide and short traces for the main current paths.
The input capacitor should be placed as close as possible to the IC pins VIN and GND. This is the most critical component placement.
The VOS line is a sensitive high impedance line and should be connected to the output capacitor and routed away from noisy components and traces (e.g. SW line) or other noise sources.