As portable and handheld products shrink in size, designers are challenged to use smaller batteries to power these products. Smaller batteries mean that the whole system must be more energy efficient. Microcontrollers (MCUs), often the ?brains? of portable or handheld products, are typically the system component that consumes the most power. Therefore, the trend in the semiconductor industry has been to design and manufacture lower power MCUs, benefiting not only original equipment manufacturers (OEMs) and individual consumers, but society at large. This article discusses the far-reaching impact of lower-power devices on electronic products, particularly those that are battery powered.
Examples of end products and systems that require low power consumption are shown in Figure 1.
Figure 1 ? Typical ?Low Power? Products
Low power consumption is beneficial for several reasons. In portable and handheld products, low power consumption equates to extended battery life. This is clearly a desirable attribute for consumers as well as a competitive advantage for OEMs. For products that are not battery powered, power consumption is still important as the less energy consumed, the lower the operating costs and the fewer environment-unfriendly emissions.
The Need for Energy Efficiency
In the United States, coal is the largest single energy source used to generate electricity. Fifty-two percent of the United States? 3.8 trillion kilowatts of electricity that was generated in 2000 was generated using coal-fired power plants. By developing products that consume less power, the obvious conclusion is that the environmental pollution from coal-fired power generation can be reduced. The other main sources of electricity generation are nuclear power (20% of the total) and natural gas (16%). Figure 2 illustrates the mix of electricity used in the United States in 2000 as well as the average electrical retail prices for the consumer.
Figure 2 ? Share of Electricity Sales and Average Retail prices
From Figure 2, we can determine that the most electricity is being consumed in residential settings and that it is the most costly energy source to residential consumers. However, each category of consumer has an incentive to use less electricity. Naturally, residential consumers want to reduce the size of their electric bill. Commercial consumers (such as offices and retail establishments) also want to reduce costs, but they have other considerations such as back-up systems that use a sizable amount of energy. If the magnitude of a power budget for an office building can be reduced, a smaller, more efficient localized generator may be used for back-up or even primary energy source. Industrial consumers are equally concerned about the costs of their energy supply and the efficiency of any potential back-up solutions. The ?other? category includes things like street and highway lighting, railroads, etc. As with the other categories of consumers, efficient energy is important for ?other? users as many of these systems (such as street lighting) spend a considerable amount of time consuming energy.
Even the automotive industry has a strong interest in reducing electrical power consumption. The modern automobile includes numerous electronic control systems that are connected to the electric system within the vehicle (today, this is a 12V battery). One example of why power consumption is of critical importance for an automobile is the airbag system. In the event of a collision, it is plausible that the electrical network becomes isolated from the battery. If this happens, the airbag control system has only a few milliseconds to determine that a collision has occurred and must fire the appropriate airbags using residual power only. For this reason, designers of automotive electronic control systems must pay careful attention to using low power consuming components.
Battery Powered Electronics
We have established that nearly all consumers could benefit from products that use less power. It saves money and it is better for the environment. Furthermore, OEMs of products that are battery powered understand that it is more convenient for the consumer if the battery life can be extended. Battery powered products are composed of a collection of power consuming devices as illustrated in Figure 3.
Figure 3 ? Power Consuming Components of a Battery-Powered Product
The typical battery-powered product includes communications systems such as radio frequency circuits, a MPU or MCU, data storage capability such as memory chips, and an interface to the user. For consumers of battery-powered products, there are several important attributes: performance, price, convenience, portability and availability. For example, the most popular cellular phones are inexpensive, need infrequent recharging, are small and ergonomically pleasing as well as having excellent operating performance with a clear signal.
These consumer requirements are driving suppliers of semiconductors to deliver products that can enable this type of functionality, while also enabling longer battery life. An ideal ?low power? component must consume very little power when it is in a ?standby? state (as this number approaches zero, it becomes more desirable) but must be able to quickly switch on and reach peak performance almost instantaneously. An example of a newer semiconductor product line that offers this is the new family of HCS08 microcontrollers. These devices were designed specifically to extend battery life as well as provide very high performance.
Figure 4 illustrates the operating profile of a hypothetical battery-powered product that uses a HCS08 MCU. Power consumption is represented on the Y-axis and time is represented on the X-axis. The product in question starts off in a standby state. This mode could be used on a product such as a remote control unit that remains powered down until a button is pressed. In order to optimize battery life, it is desirable to stay in Stop 1 mode for as long as possible as this has the lowest current consumption, therefore the lowest power consumption.
Figure 4 ? Operating Profile of Hypothetical Low Power Product
The diagram then shows a transition from Stop 1 mode to Run Mode. This change in operating mode would occur when the MCU is required to ?wake-up? in order to check the external environment. For example when a wireless mouse for a PC is moved, it recognizes movement and a transition occurs from Stop mode to Run mode due to the externally generated stimulus.
The next transition on the diagram indicates that the MCU enters Stop 2 with AWT (Auto Wake-up Timer) enabled. This is an operating mode that is used so that a product can wake itself up without requiring external stimulus. A smoke detector, for instance, regularly wakes itself up in order to read the condition of the internal sensors. If the MCU determines from the data transferred by the sensor that no action is necessary, it will put itself back to sleep (e.g. Stop 1 mode) ? thus spending as little time as possible consuming power. The diagram shows that the MCU will wake itself up from Stop mode to Run mode at regular intervals in order to perform these types of checks.
The peak that is shown in the middle of the chart represents a transition from low power Stop to Run mode with maximum performance. Although it is generally better to consume less power, sometimes there is a need to process a lot of data very quickly to determine what is going on and to take appropriate action. This would be especially true when it is important to take very quick action in systems like alarms. The HCS08 can be ramped very quickly from Stop mode to its full operating speed of 20 megahertz in order to accomplish this. This operating speed is sufficient to ensure that any data can be processed extremely quickly, therefore allowing the device to get back into a low power mode as quickly as possible. This helps to optimize overall power consumption and extend battery life for the end-product.
A die photograph of a HCS08 microcontroller is shown in Figure 5. As well as providing a fast operating speed and a number of operating modes for low power consumption, this MCU has been designed to minimize external components such as clock circuits, crystals, programming charge circuits and protection components. This reduced number of components ensures that overall power consumption is minimized.
Figure 5 ? HCS08 ?Extended Battery Life? Microcontroller
Finally, it is worth noting that the functionality requirements for portable and handheld products will continue to increase over time, at a faster rate than electronics-based products in general will grow. Consumers are demanding ? and advances in semiconductor technology have enabled — bigger and better color screens, more intuitive user interfaces, faster performance, more wireless interconnectivity, and smaller and more portable form factors. This means that for the same battery size and battery lifespan, all types of electronic products must take advantage of low power semiconductor devices in order to incorporate more features while consuming less power. As the industry continues to develop more power-efficient components, each segment of society that pays to consume power will benefit.