A Fast Transient Current-Mode Buck Converter With Linear Regulation Mode

This article proposes a configurable supply mechanism in the power stage to simultaneously improve the load transient response and power conversion efficiency. The power stage, comprising a dc–dc converter and an auxiliary power circuit (APC), can be organized depending on the variable load conditions. During step-load changes, the APC can provide an additional charging or discharging current to the output capacitance of the dc–dc converter to compensate for any differences between the load current and inductor current. Meanwhile, two auxiliary transient transistors are employed to immediately adjust the output level of the error amplifier because the peak current-mode control is used in the dc–dc converter. Thus, the recovery time and output transient ripple are enhanced significantly. At the steady state, the APC is inactivated; thus, the conversion efficiency of the dc–dc converter does not degenerate. Above medium loads, only the dc–dc converter is activated to deliver adequate power with high efficiency. At light loads, the APC acts as a linear regulator to take over the energy delivery scheme because power consumption is reduced effectively while the output voltage is kept. Therefore, the hybrid operation can guarantee improvements in load transient response and power conversion efficiency at light loads. The proposed converter was fabricated with 0.35-μm CMOS technology. The experimental results showed that the recovery times for 450-mA step-down and step-up loads are 1.6 and 2.0 μs, respectively. Comparing to when the transient mode is disabled, the recovery time of the output voltage is improved by over ten times when the transient mode is enabled. Further, the efficiency improvements with the proposed method at load current of 20 mA under the output voltages of 2.5 V and 1.8 V are 13.8% and 4.9%, respectively.