Makes the battery life of up to 20 years of energy-saving design of micro-controllers (1)

In the design of battery-powered products, people obviously hope that battery life should be as long as possible.

As a quick development of device categories from a single battery developed application not only in specifications: but to the entire product concept. Energy-sensitive applications roughly divided into energy metering systems, home and building automation, security and medical system (Figure 1). These products are usually organized around a microcontroller (MCU), must operate with a single primary batteries for a long time. In some applications, to replace the battery is very difficult or even impossible: in other applications, end users are not willing to pay the cost of replacing the battery.

In this application is very low duty cycle is active in the microprocessor, in "deep sleep" State time may account for 99 per cent-or even higher, reaching 99.9 per cent are not rare.

Microprocessor in a periodic cycle, or in response to certain stimuli was "wake up" to perform the operation and return to sleep. Because they spend so much time to go to bed, it is clear that for the longest battery life of the key parameter is in power-down state of the current consumption. However, the same section of the battery life for three or four years and more than 10 years, be extended to 20 years or even longer time difference is to pay close attention to the task of how to use the MCU resources of each, and how the design of the MCU itself in various ways to reduce energy consumption.

A one-cell 20 years

CR2032 battery used in small MCU as remote environment sensor, this is a lithium manganese dioxide/3V primary batteries.

Typical vendors-for example, Kodak (reference 1)-evaluation of 230 mAh to end point voltage power 2V 5.6 k (approximately 0.5 mA). In that case, the battery life will provide 400 hours, by contrast, energy sensitive application enables service life up to 20 000 hours. This special type of battery has good shelf life or self discharge rate, the datasheet displays 10 years after its capacity of up to 90%. It is very similar, this corresponds to A continuous charging about 0.25, if you are able to reach 10-20 years of battery life, the application of the General requirements are met.

With the battery life is a limited number of charge, the designer must in all phases of operation of MCU reduces product of current and time, not only to reduce the number of each µA, and also to reduce every action of every microsecond.

In order to reduce the deep sleep mode current consumption, energy sensitive applications in 8-bit MCU (or 16-bit) kernel is very common.

The reason is that the 8-bit kernel — even in the latest version also often use this design--a small, gated relatively small, static or leakage current low. However, many applications now require more than 8-bit kernel more processing power. In other application areas, MCU users tend to choose from an 8-bit upgrade to a 32-bit environment. In the case of low power consumption, people always assume that the 32-bit kernel in its power-down mode when you use the current state is unacceptably high. With the full range of low power design technologies, today's IC designers already may have a 32-bit ARM kernel provides different low-power mode, with its 8-bit competitors as good or even better, but also can achieve fast wake-up time. 32-bit processors more processing performance also enables the MCU can more quickly complete the task, so that in these low-power mode to spend more time to further reduce the average power consumption.

Low power peripherals functionality

To optimize the lowest consumption power MCU sleep power consumption need overall design approach.

In addition to the kernel, the MCU in the other modules in standby equipment, regulator, bias current generator, undervoltage detection comparator, power-on reset circuit will continue to attract some of the current. In almost all cases, simple alternation is applicable; Power-down state, the more peripheral functions are completely cut off, chip ready to implement processing tasks wake-up time. Due to the application of very different, MCU designers a flexible power off State expansion kit form is very important, so that product designers as well as his personal project for standby power and responsiveness for alternating transposition.

Design implementation arm core to achieve in the deepest sleep nanoamp district in the State of the current level is only a low energy strategy.

Provides a 32-bit kernel processing power to control energy use has opened up a new way, at any time, it is MCU area below the power figure, over time, it was taken away from the battery charge (Figure 2). Is this specific configuration of the current consumption of the headline figure, the more designers will have to pay close attention to maximize battery life. In EFM32 microcontroller Development Kit, this measurement is very clear; The basic functionality of this kit is its advanced energy monitor (Figure 3). The facilities in the fill current rail MCU cores in measuring current; one from the analog to digital converter (ADC) voltage through the resistor, and collecting a Development Kit software integrate their readings to accurately measure the power at different times.

　　

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