OK, an easy one for a change
: Multiphase buck with synchronous rectification.
The idea is simple: connect a number of regular buck circuits in parallel and organize a phase difference between them. Say you operate 3 parallel ones; then their switches will be operated with a 120 degree phase shift.
For efficiency, the freewheel diode is replaced with a FET switched in synchrony with the main switch to minimize diode conduction and recovery losses.
Probably easy to locate a suitable controller from the numerous devices offered by DK, Mouser, Farnell &c.