Critical inductance in voltage regulator modules

Multichannel interleaving makes it possible to use small inductances to improve voltage regulator modules' (VRMs) transient responses. However, smaller inductances reduce efficiency. Analysis shows that the transient responses are not only determined by the inductances but also the control bandwidths. This paper presents the concept of critical inductance in VRM. Critical inductance is the largest inductance that gives the fastest transient responses. Critical inductance is a good reference for optimal VRM design. Critical inductance is a function of the feedback control, the step current magnitude and the steady-state operating point.