A Fixed-Frequency Quasi-<formula formulatype="inline"><tex Notation="TeX">${\rm V}^{2}$</tex></formula> Hysteretic Buck Converter With PLL-Based Two-Stage Adaptive Window Control

This paper proposes a fast transient quasi- V ² fixed-frequency hysteretic buck converter designed and fabricated using TSMC 2P4M 0.35-μm CMOS process. The proposed converter can achieve fixed frequency switching through a novel phase-locked-loop-based two-stage adaptive window control. Under ultralight load conditions, the proposed converter operates in a pulse frequency modulation mode to reduce the switching loss and improve light load efficiency. A quasi- V ² technique is applied for obtaining inductor current information without relying on an output capacitor with a high equivalent series resistance; therefore, the output voltage ripple can be reduced. The experimental results show that the proposed converter can operate at a load current ranging from 18 to 700 mA, a supply voltage ranging from 2.7 to 4.2 V, and an output voltage of 1.2 V. The off-chip inductor and output capacitor are 2.2 μH and 10 μF, respectively. Through the PLL control, the switching frequency is maintained at 1 MHz. The transient response time is approximately 5 μs, and the highest efficiency registered is 95.6%.