Uncovering the secrets of the long battery life of CES wearable innovations

    Wearable devices were undoubtedly one of the highlights of the Consumer Electronics Show (CES) in Las Vegas, USA, earlier this year. However, some analysts believe that "CES 2014: smart wearables have hot spots but no bright spots" because no product can make consumers fall in love with it at first sight. Does this count as a cold shower on wearable devices? In fact, the situation is not that bad. The Magellan Echo smart sports watch, which won the "CES 2014 Innovation Design and Engineering Award", is a bright spot, standing out for its innovative design and excellent battery life (it can run for up to 11 months under the condition of a single CR2032 button battery).

    This sounds incredible, running for up to 11 months on a single CR2032 button battery! And the performance is far better than other similar devices, which means that Echo does not sacrifice performance in exchange for ultra-low power consumption. Is it that energy is not conserved? Of course not! Steven Zhang, product manager of Shiqiang, the core agent of Silicon Labs in China, revealed to us the secret behind the extremely long battery life.

EFM32——The world's most energy-efficient 32-bit Cortex-M MCU is the hero behind the scenes

    “The 32-bit Giant Gecko MCU based on the ARM Cortex-M3 core plays a critical role in the energy efficiency of the Echo sports watch. Their ultra-low power goal is achieved by optimizing the five different energy modes of the Giant Gecko MCU and leveraging the MCU’s Low Energy Sensor Interface (LESENSE) and Peripheral Reflex System (PRS). These features enable energy-efficient and autonomous peripherals to handle timing and sensor control without CPU involvement,” explained Steven.

    Giant Gecko MCU belongs to Silicon Labs' Gecko series. In the camp of ultra-low power MCU, the name of the little gecko is very famous. However, have you ever thought about why such an electronic product is named after a small animal?

Figure 1. Why is EFM32 called Little Gecko?

    It turns out that in nature, the energy consumption of a gecko is only 10% of that of a mammal of the same size. A performance comparison with the top 10 low-power microcontrollers on the market today proves that the EFM32 microcontroller consumes only a quarter of the energy of other similar 8-bit, 16-bit or 32-bit microcontrollers. This is equivalent to extending the life of a typical 3V button battery by at least 300%, or 7 years. In short, the EFM32 MCU, like this cute little gecko, is the king of power saving in the field of microcontrollers.

Does low power consumption mean high energy efficiency?

    In order to achieve the goal of high energy efficiency, EFM32 breaks the design convention of microcontrollers and adopts a completely different design approach.

    “There are too many MCUs in the industry that claim to have the lowest power consumption, but EFM32 does not emphasize low power consumption. Instead, it focuses on the concept of highest energy efficiency. This is because low power consumption does not mean high energy efficiency. Our ultimate goal is to achieve ultra-long battery life, and high energy efficiency is the key to achieving this ultimate goal.” Steven pointed out.

    Power consumption and energy consumption are two completely different concepts. Power consumption only represents the magnitude of instantaneous current at a certain point in time, while energy consumption is equal to the product of power consumption and time, as shown in Figure 2. Whether a system is power-saving depends on whether its overall energy consumption is low enough.

Figure 2. Relationship between power consumption and energy consumption.

    Working mode power consumption, standby mode power consumption, and duty cycle are the three key parameters that determine MCU energy efficiency. The total energy consumption of a system is equal to the sum of working mode energy consumption and standby mode energy consumption. In actual applications, the energy consumption of standby mode is much lower than that of working mode. For general MCUs, the energy consumption in these two modes is basically fixed. In order to save power, the most common method we use is to shorten the duty cycle of the working mode as much as possible while ensuring the normal function of the product. So, is there a better way?

    As shown in Figure 3 below, there are four colored boxes, representing the power consumption of four different MCUs when executing the same functional program. As can be seen from the figure, the working curve represented by the MCU represented by the green box is very special. Not only is the power consumption in sleep mode lower, the execution speed and wake-up time are faster, especially the power consumption in working mode has been greatly reduced many times, while the other three MCUs are a parallel curve throughout the working mode, and the power consumption is basically fixed. From the perspective of overall energy consumption, the green MCU is obviously more power-saving than the other three MCUs. This is the result of the high energy efficiency that the EFM32 represented by the green box can bring.

Figure 3. Working curves of four different MCUs when executing the same functional program

10 factors that contribute to EFM32's high energy efficiency

    Silicon Labs' energy-friendly EFM32 32-bit microcontrollers outperform existing low-power MCUs - here, we highlight 10 factors that make this possible. As shown in Figure 4 below, these 10 factors include: 1. Very low active mode power consumption; 2. Reduced processing time; 3. Fast wake-up time; 4. Ultra-low standby current; 5. Autonomous peripheral operation; 6. PRS - Peripheral Reflex System; 7. Well-designed energy modes; 8. Energy-saving peripherals; 9. LESENSE - Low-power sensor interface; 10. Simplicity Studio and advanced energy monitoring modules.

Figure 4. Ten major technical features of the EFM32 32-bit microcontroller.

    “Among these 10 factors, PRS is a very distinctive peripheral reflex system of EFM32. The peripheral reflex system in the microcontroller can directly connect one peripheral device to another peripheral device without using the CPU. When the CPU is in sleep state, the peripheral device can generate a trigger signal through this system, and other corresponding peripheral devices can receive this signal and respond to it immediately.” Steven pointed out.

    Well-designed energy consumption modes are also a major innovation of EFM32 in terms of high energy efficiency. The internal structure of EFM32 is shown in Figure 5 below. As shown in the upper right corner of the figure, there are five rings of different colors, representing "0, 1, 2, 3, 4", which represent the five energy modes of EFM32. Corresponding functional modules can be used under different colors, and the coverage of the modes can be backward compatible. For example, in EM2 mode, only the light blue, dark blue, and black rings in the figure can be used, while in EM4 mode, only the black circles can be used.

Figure 5. EFM32 internal architecture

    The five power-saving modes of the EFM32 microcontrollers provide system designers with the design flexibility to optimize their applications for highest performance and longest battery life.

Shiqiang provides EFM32 product support to help IoT applications

    The 32-bit EFM32 has defeated existing MCUs to become the world's most energy-efficient microcontroller. Its original design intention is to save energy and power, and it is mainly aimed at battery-powered product applications, such as smart meters, smart homes, security systems, healthcare, and portable handheld systems such as RFID, especially applications that have strict requirements on the battery life, such as requiring the battery to be non-replaceable for at least 3 years, 5 years or even 10 years.

Figure 6. Market applications of EFM32.

    Silicon Labs acquired Energy Micro in 2013, which was a milestone for Silicon Labs. This acquisition greatly expanded Silicon Labs' microcontroller product line and added nearly 250 ARM-based EFM32 Gecko microcontroller products. As Silicon Labs' core distributor, Shiqiang naturally benefited from this acquisition and strengthened its strength in ultra-low power MCU products.

Figure 7. Shiqiang provides a wide range of EFM32 product options and technical support.

    As shown in Figure 7 above, the EFM32 MCU Roadmap is divided into three categories according to the core: M0+, M3, and M4. Among them, the M3 series is the most abundant, with four series from low-end to high-end, including: Tiny, Gecko, Leopard, and Giant. The high-end can also support TFT and USB functions, and the maximum flash can support 1Mb. The smallest package is QFN24.

    “From M0+ to M4, all models of EFM32 MCU are software compatible. Different models with the same suffix are pin-to-pin compatible, so it is very convenient for subsequent platform upgrades.” Steven finally emphasized, “Shiqiang will provide you with EFM32 product selection and related technical support, which can completely relieve your worries and help you.”