Critical inductance in voltage regulator modules

Multi-channel interleaving makes it possible to use small inductances to improve voltage regulator module´s (VRM´s) 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 the VRM optimal design. Critical inductance is a function of the feedback control, step current magnitude, and steady-state operating point