Wireless sensor nodes function as an interface that sense, transmit/receive information, and to actuate a physical environment. These sensor nodes are typically powered using a coin cell battery or an energy constrained harvesting source, to support a smaller form-factor. Internet of Things (IoT) applications that are operating under such energy constrained environment typically use a heavily duty-cycled operation of its sensor nodes to maximize their battery lifetime to > 10 years. With the duty-cycled operation of power hungry blocks such as radio transceivers, MCU & sensors, the always ON power management circuits serve as the limiting factor to achieve an increased battery lifetime. This course discusses the power management unit specifications and its requirements to support an ultra-low power IoT sensor node application. In particular, circuit design techniques to achieve high power conversion efficiency across a wide dynamic range of load currents, ultra low power voltage reference and timer circuits, and energy metering circuits are discussed in detail.