Dynamic Bus Voltage Reconfiguration in a Two-Stage Multiphase Converter for Fast Transient

This article proposes a dynamic bus voltage transition method in a two-stage multiphase buck converter for 48-V-to-point-of-load (PoL) applications. The proposed topology uses a bank of precharged switching capacitors at the output of the first-stage buck converter. This configuration helps to achieve an immediate intermediate bus voltage transition while supplying a (second-stage) multiphase buck converter. This can substantially speed up a large-signal transient recovery by adjusting the bus voltage to its highest voltage level. Thereafter, near steady state, the bus voltage is set to its (lower) optimum value for improving the overall efficiency of the two-stage architecture. A higher bus voltage can reduce the output capacitance for the second-stage while retaining the (voltage) undershoot within the desired limit, which can reduce recovery time and current overshoot during a step-reference transient. The first stage operates in the open loop, while the second stage uses mixed-signal current mode control using a field-programmable gate array (FPGA) device. A hardware prototype of the proposed architecture is made, and an improved performance is demonstrated using simulation and experimental results.