Ultra-low power system for wearable devices

February 23, 2015 //By Chris Glaser
Ultra-low power system for wearable devices
Chris Glaser, Applications Engineer, Texas Instruments considers an ultra-low power system for wearable devices.

While the brains of the typical wearable device might be the embedded microcontroller (MCU), the heart is definitely with power management. Extremely small capacity batteries, diverse array of functions needing power, and the incredibly small solution size force new and innovative power management solutions to make the system work well. But when an ultra-low power optimized MCU and ultra-low power optimized DC/DC converter come together, the result is a well-running, well-oiled machine fit for wearable applications.

Wearable systems

A wearable device brings together multiple facets of engineering, beginning with the MCU and its integrated features and peripherals. Temperature sensors, analog-to-digital converters (ADCs), display drivers, a Bluetooth® Low Energy (BLE) radio, and even encryption are frequently integrated into the MCU. Other sensors such as accelerometers or pressure sensors are usually implemented discretely due to their system-specific nature. The MCU and sensors define the features and capabilities of the wearable device, which gives it its appeal and niche in the market.
 
For a very small wearable device, the heart of the system is the power management. A wearable device can lose its appeal if it must be recharged multiple times a day or has a heavy battery pack. Achieving multi-day run times and keeping the device small and light requires ultra-low power-optimized power management to efficiently convert the battery’s limited energy to useable power by the loads. Figure 1 shows a typical block diagram for an optical heart rate monitor with the MCU, sensors, BLE radio, power management, and battery.

Figure 1. Optical heart rate monitor block diagram with MCU and power supply. The MCU integrates most of the required functions in a typical wearable device. The power supply integrates all the required components for a complete DC/DC converter solution. Included is a load switch for simpler and smaller system integration.
 
Ultra-low power microcontroller

 
While the MCU must provide a diverse array of functions for the wearable device, it

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