Small Signal Modeling of a High Bandwidth Voltage Regulator Using Coupled Inductors

Today's voltage regulator (VR) for the microprocessor requires a current loop to achieve adaptive voltage positioning and phase current sharing. A fundamental limitation, current loop sample hold effect, limits the control bandwidth to be pushed beyond 1/6 of the switching frequency. This paper reveals the limitation of the control bandwidth of a two-phase buck converter using peak current control scheme. The limitation can be overcome by coupling the two output inductors. A new small signal model is proposed to study the sample hold effect in coupled-inductor implementations. The relationship between the coupling coefficient and the sample hold effect is then discussed. Based on these understandings, a strongly coupled two-phase buck converter has double the bandwidth of the noncoupled VR; and this is experimentally verified

[1]  Milan M. Jovanovic,et al.  Design considerations for 12-V/1.5-V, 50-A voltage regulator modules , 2000, APEC 2000. Fifteenth Annual IEEE Applied Power Electronics Conference and Exposition (Cat. No.00CH37058).

[2]  Peng Xu,et al.  Investigation of candidate VRM topologies for future microprocessors , 2000 .

[3]  Fred C. Lee,et al.  Design considerations for VRM transient response based on the output impedance , 2003 .

[4]  Peng Xu,et al.  Performance improvements of interleaving VRMs with coupling inductors , 2001 .

[5]  R. B. Ridley,et al.  A new, continuous-time model for current-mode control (power convertors) , 1991 .

[6]  F.C. Lee,et al.  Analysis of the power delivery path from the 12 V VR to the microprocessor , 2004, Nineteenth Annual IEEE Applied Power Electronics Conference and Exposition, 2004. APEC '04..