In a multiphase buck converter running at precise duty cycles which have an inverse
integer relationship with the number of phases and a precise synchronized phase
relationship, it is possible to have zero output ripple. If the output inductors
are replaced with coupled inductors having nominally the same inductance, and the
second windings of the inductors are wired in a loop with correct phasing, under
steady state conditions the voltage drop around the loop will be zero. A small
voltage injected into the loop can cause very fast transitions in current in the
loop, and those currents will be reflected to the first windings of the inductors
as a very rapid transition in the output current. This converter has no dc voltage
control capability, so it is preferably used with a pre-regulation stage as the
control of the dc output voltage. Dynamic voltage control is very fast, as the
current into the output capacitor can change very rapidly.
