Bandwidth improvements for peak-current controlled voltage regulators

To ensure the current sharing among the interleaved phases, the peak-current control is widely used in the voltage regulator (VR) applications. Meanwhile, to save the cost and footprint by reducing the output capacitance, high control bandwidths are mandatory. Because of the sample-hold effect in the peak-current loop, there exist stringent challenges to the high-bandwidth designs for VRs. In this paper, the influence from the sample-hold effect is investigated to clarify the difference between the VR and conventional applications. After that, two approaches for higher bandwidth are introduced. To decrease the phase delay due to the sample-hold related double poles, excessive external ramps are inserted to the modulators. To increase the effective sampling frequency, the phase inductor currents are coupled, either by the coupled-inductor structure or through the feedback control. In addition, a small-signal model including the sample-hold effect is derived for the coupled-inductor buck to explain the improvement. High-bandwidth designs are verified by the simulation and experimental results. A bandwidth of one-third switching frequency is demonstrated with a coupled-inductor VR.