TI layout recommendations for the TPS62821 and TPS63805YFF switcher ICs show placing the input capacitor (TPS62821) and input and output capacitors (TPS63805YFF) between the switcher IC and the switching inductors. From an RF standpoint, the placement of the capacitor(s) and inductor will introduce some feedback into the filter capacitors. Also, the inductor is forced to be farther from the switching IC creating longer traces to the inductors, thereby generating and receiving more noise, especially on the high current versions of the ICs.
The TPS63805YFF design butts the input and output caps directly against each other. This way input ground noise is fed into the output ground, resulting in ground noise transfer from the input directly to the output. This noise feedback could introduce oscillations.
