Adaptive frequency-controlled ultra-fast hysteretic buck converter for portable devices

This paper describes a new hysteretic buck converter including a differentiator and an adaptive hysteresis window control. Differentiating the feedback signal achieves ultra-fast switching of the proposed buck converter. The adaptive hysteresis window control allows a monotonous operation with predictable noise spectrum, and gives way to efficient design for variable supply and output voltages. The proposed hysteretic buck converter designed in 0.13 μm process operates reliably in 2.5 ~ 3.6 V V_DD range, and generates a stable output voltage ranging from 0.7 V to 2.2 V. The comparison results indicated that the switching frequency becomes quadruple times higher, and the voltage ripple is reduced to fourteenth in amplitude. They also indicated that the efficiency is improved from 1.3% to 3.4% depending on loading condition, and the normalized switching frequency variation is reduced by 73% with variable V_DD and 59% with variable V_OUT of the conventional hysteretic buck converter.