A linear 4-element model of VRM —Characteristics, practical uses and limitations

This paper discusses the characteristics and limitations of a 4-element linear model of a voltage regulator module (VRM) by comparing it with a state average model (SAM) with feedback used by Intel. A virtual load line method is proposed to correlate the 4-element linear model by introducing a modified DC resistance. The resultant impedance profile is in good agreement up to 2GHz with that by original SAM. Furthermore, it can be simplified to a 2-element model, which still gives good agreement since the high frequency impedance is dominated by the bulk capacitance in realistic PDN´s.