Design of Dual Lower Bound Hysteresis Control in Switched-Capacitor DC-DC Converter for Optimum Efficiency and Transient Speed in Wide Loading Range for IoT Application

This article proposes a dual lower bound hysteresis control (LBHC) method with frequency control for the design of switched-capacitor (SC) dc-dc converters in always-on Internet-of-Things (IoT) applications. Conventional SC control methods often face a tradeoff between speed and efficiency. Efficiency is crucial for battery life, while speed is essential for system responsiveness. This article aims to use the proposed method to achieve frequency-independent regulation of the output dc level. This helps achieve a fast response time at the system level by tuning controller frequencies without compromising stability. Furthermore, the proposed dual LBHC loop guides frequency and power scaling, ensuring consistent efficiency over a wide range of load currents through two clock-gated comparator operations per clock cycle. By analyzing the operating principle, this article also discovered that designing the dual LBHC based on its maximum load current point can guarantee its stability over the entire load range. To illustrate this concept, a fully integrated 2:1 capacitive dc-dc converter was implemented using a 180-nm CMOS process. The results demonstrate guaranteed efficiency of at least 75% across load current ranges up to 228x, with a peak efficiency of 80.4%. In addition, an active response time of 80 ns is achieved during load transients ranging from 0.04 to 4 mA.