DC-DC Voltage Conversion for Low Wake-Up Energy Applications: Design Considerations and Implementation

As the global phenomenon of the Internet of things increasingly influences our daily life, battery-powered smart devices require advanced power management strategies to maintain and possibly extend their battery lifetime. These devices often include power-hungry elements such as signal converters, actuators, transceivers and microcontroller units (MCUs). Integrated power management units (PMUs) generate the required voltage domains and supply all the elements that are present in a device. Therefore, their role is key to reduce the energy consumption of the MCU in all conditions and operational modes. Especially the wake-up is a demanding phase in terms of energy consumption per active cycle. This work presents a new approach for the design of inductor-based step-down DC-DC converters for integration in the PMU of an ultra-low power (ULP) MCU. The proposed converter is designed to improve the energy efficiency at system level by reducing the wake-up energy and start-up time of the supplied core. The use of a minimized output capacitor for the implementation of the presented DC-DC converter enables an unprecedented reduction of the wake-up energy. The controller of the proposed DC-DC converter is based on a predictive peak current control that allows the system to control the energy transfer at extremely low power consumption. The wake-up energy has been reduced up to three orders of magnitude as compared to state-of-the-art DC-DC converters. The proposed design approach overcomes the limitations of standard DC-DC converters for ULP applications. The reduction in wake-up energy and start-up time meets the performance of well-known start-up energy-efficient converters such as low drop out (LDO) regulators.