Wearable devices are integrating more and more functions, which poses challenges for power management. The battery in wearable devices is usually very small, and the device needs to work for a long time without charging, so power consumption is a key design consideration. To ensure the fashionability of wearable devices, circuits need to be kept within extremely small sizes, which makes power management and other devices more inclined to adopt single-chip solutions. In order to cope with the difficulty of battery technology to solve the demands of battery life, wearable devices may use new power sources, such as solar energy or thermal energy for energy harvesting.