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upstream, forcing users to monitor, charge, or replace batteries, for example. Although users reluctantly accept those tasks for smartphones, fitness devices, and other personal electronics, IoT device developers cannot so easily defer responsibilities. Yet, IoT device developers face a deep set of challenges for meeting these fundamental requirements. Satisfying the broad need for better information means developers have to deliver IoT device designs with maximum capability and minimum power consumption—all without compromising fundamental user expectations for low cost, small size, and necessary security. The need to meet the requirements of upstream analysis drives an inevitable increase in software complexity and code footprint, requiring more powerful microcontrollers (MCUs) capable of meeting traditional needs for sensor data acquisition as well as emerging needs for local data analysis at the IoT periphery. Yet, the computational power and integrated capabilities of an MCU might not be enough to solve the designers' dilemma for balancing power and performance in power-constrained IoT designs. Instead, the solution lies in designs that combine power-efficient MCUs with power management integrated circuits (ICs) capable of complementing battery power with harvested energy from ambient sources. MCUs typically dominate power consumption in most designs, IoT devices included. Consequently, power optimization for these devices starts with an MCU such as Analog Devices' ADuCM4050, which provides designers with a wealth of features for meeting tight power budgets. As with most advanced MCUs, the ADuCM4050 provides multiple low-power operating modes that reduce overall power consumption by gating clocks to hardware blocks or removing their power entirely. A special ADuCM4050 power mode, Flexi mode, offers an effective compromise between normal active mode and the ultra-low-power sleep state typically available in advanced MCUs. In Flexi mode, the ADuCM4050's power management subsystem turns off the MCU's ARM Cortex-M4F core but keeps its integrated peripherals active. As a result, developers can initiate direct memory access (DMA) transfers for sensor data acquisition, waking the core only when complete data is ready for further processing. Because the ADuCM4050 can wake from Flexi mode in only about 1.6μs, developers can utilize Flexi mode without impacting response time or throughput for all but the most time-critical applications. As even this simple example suggests, creating a power-efficient IoT design requires more than coarsely switching an MCU to its lowest possible power mode. It requires a development approach that builds power optimization into the fabric of the design, applying a level of application awareness to find the proper utilization of MCU power management features. The most effective approach for developing an IoT device capable of sustained operation on a single battery depends heavily on target requirements for sampling rate, resolution, latency, throughput, and more. Even so, developers can provide their designs with a significant safety margin for extended battery operation by supplementing battery power with energy harvested from the ambient energy that bathes nearly every IoT device. Analog Devices' LTC3330 and LTC3331 energy harvesting ICs provide developers with a simple solution for maximizing battery life in IoT designs. Each device integrates a full-wave bridge rectifier, control circuitry, and buck- boost switching regulator. Along with that common foundation, the LTC3330 includes a power selector capable of switching a load's power source from a primary battery to harvested power when available. The LTC3331 includes a battery charger for an attached rechargeable battery, switching power to the battery when harvested power falls below threshold. 20 For IoT device designers, the availability of low-power MCUs and energy-harvesting power-management ICs offers a particularly effective solution for building sensor systems capable of extended operation on battery power. Using the advanced power- management features of the ADuCM4050 MCU in combination with the energy- harvesting LTC3330 battery extender or LTC3331 battery charger, developers can meet the multiple challenges associated with emerging IoT applications that depend on a growing class of battery-powered IoT devices. Summary IoT