Proper power integrity (PI) analysis is essential for modem electronics devices to minimize voltage noise. The low- frequency response of a power distribution network (PDN) is determined by the voltage regulator modules (VRMs) installed on the board. However, the conventional VRM model is either represented by an over-simplified passive circuit or an encrypted model provided by then vendor. These models can only work for limited operating conditions. In this paper, a generic average model for up-to-date DC converter is proposed. Both time and frequency domain responses of a current-mode buck converter with adaptive on-time control (AOT) method are captured by the proposed model. This cycle-by-cycle averaged model can be extended for converters with other control methods.