Microcontrollers Improve Power Efficiency of 8051-Based Designs - Application Note - Maxim

High-speed microcontrollers are widely used in portable equipment. With the proper use of a power management mode, the designer can optimize the life of batteries used in today's new systems. This application note looks at ways to reduce power consumption by choosing efficient clock source and clock speed, the use of stop mode, idle mode and burst mode. The Maxim High-Speed Microcontroller and Ultra-High-Speed Flash Microcontroller families provide the user with advanced features for batterybacked applications. Portable products continue to advance in features and capabilities. Customers are demanding more performance out of their products, which requires greater computing power. At the same time, they want products with less power consumption. At the heart of these competing demands is the microcontroller, which is typically one of the largest power consumers in portable instruments. Low-power processors exist, they are often limited in performance. The high-speed microcontroller family from Maxim is a good compromise of power and performance. It is based on the 8051 architecture, one of the most popular microcontrollers in the world. Designers prize its ease of use, rich I/O structure, and wide acceptance. Its prevalence has carried over into the portable arena, where it has found a home in many applications. This article addresses approaches to minimizing power consumption using 8051 controllers, with emphasis on new architectural improvements that can extend the battery life of high-performance 8051based designs. Integrating peripherals on-chip and selecting the proper clock source are discussed as ways to reduce power consumption. Software techniques for power conservation are presented, as well as a method of reducing power consumption in systems that use Stop mode. Clock Speed The most important factor in determining power consumption in any microcontroller design is the system clock speed. The power consumption of complementary metal oxide semiconductor (CMOS) devices is directly proportional to clock speed. It follows, then, that it is beneficial from a power standpoint to run a processor at the slowest speed possible. Figure 1 shows a typical power curve for a generic 8051 microcontroller, a relationship known to all portable system designers. In general, the current vs. frequency characteristic is linear, with a DC offset.