Wearable devices, from smart watches to portable health and fitness trackers, are changing many aspects of our daily lives. A successful wearable device must deliver the right combination of price, performance, functionality and battery life, as well as a unique look, feel and behavior to differentiate itself from its competitors.
To reduce the microcontroller’s impact on the wearable platform’s energy budget, it is important to minimize the frequency and duration of any task that requires it to awaken from a low-power sleep mode. One of the primary ways to optimize a low-power embedded design is to find an MCU offering the lowest sleep mode that still provides adequate response to real-time events. Most MCUs using the ARM Cortex®-M processing core support multiple sleep modes.
Powering some of today’s hottest wearable products such as the Misfit Shine and the Magellan Echo smart sports watch, our EFM32 Gecko microcontroller family uses standard 32-bit ARM Cortex®-M cores combined with an energy-optimized set of peripherals and clocking architecture.
The EFM32 architecture has been designed from the ground up specifically for energy-sensitive applications. The architecture features a range of power modes that enable developers to achieve the optimal energy efficiency required by wearables.
- Sleep/Standby (Known as EM1 mode for EFM32 MCUs) – Enables quick return to active mode (usually via interrupt) at the expense of slightly higher power consumption. In this mode, power consumption for EMF32 = 45 μA/MHz; typical equivalent 32-bit MCU = 200 µA.
- Deep Sleep – (EM2 mode for EFM32) – Leaves the MCU’s critical elements active while disabling high-frequency system clocks and other non-essential loads. In this mode, power consumption for EMF32 is as low as 900 nA; typical equivalent 32-bit MCU = 10 μA to 50 μA.
- Stop – (EM3 mode for EFM32) A deeper version of Deep Sleep Mode that enables further power savings while retaining limited autonomous peripheral activity and fast wakeup. In this mode, power consumption for EFM32 = 0.59 μA; typical equivalent 32-bit MCU = 10 μA to 30 μA.
- Off – (EM4 or shutoff mode for EFM32) – This “near-death” state preserves the minimum compliment of functionality needed to trigger wakeup from an external stimulus. The energy savings comes at the cost of significantly longer wake-up time. In this mode, power consumption for EFM32 = 20 nA (420 nA with RTC running); typical equivalent 32-bit MCU = 1.5 µA.
- Backup Battery Mode – A unique EFM32 feature that offers an attractive alternative to Shutoff Mode, preserving a few more critical functions and enabling much faster wake-up.
For additional wearable design tips, read out whitepaper: “Winning Design Strategies for the Wearables Market”
To see some of these wearables in action, watch our video on smart wearables featuring Silicon Labs technology.