Design of Enhanced Three-Level Buck Converter With Configurable Power and Control Stages for Fast Load Transient Response

This paper presents an enhanced three-level buck converter (E3LBC) with configurable power stage (CPS) and configurable control stage (CCS) for fast load transient response. Compared with the conventional 3LBC and existing solutions, the proposed CPS can raise the inductor current slope significantly by changing the switching node voltage to 3/2 times or -1/2 times the input voltage (V_IN) during the load-increasing or load-decreasing transient, which will improve the load transient response. Moreover, the CPS can realize the series or parallel operations of flying capacitors (C_F1, C_F2) and make their voltages (V_CF1, V_CF2) eventually converge to V_IN/2. On the other hand, the proposed CCS can eliminate the minimum off or on time by using hysteresis control and keep the inductor charging or discharging all the time during the load-increasing or load-decreasing transient for further improving load transient response. Besides, the CCS can provide an adaptive-on-time control in the steady state to acquire a pseudo-constant frequency for small output voltage ripple. The prototype design has been fabricated with the 0.18-μm CMOS process. According to the measurement results, the E3LBC exhibits undershoot/overshoot voltages and settling time of -19/+30 mV and 1.2/1.1 μs, when the load current is changed between 100 mA and 500 mA. The other measurements and comparisons also verify the effectiveness of CPS and CCS for the E3LBC.