Power-hungry portables eye voltage regulator

But the third and fourth generations of cellular telephones promise data streaming, enabling e-mail and Internet browsing, complete with downloaded MPEG audio and video playback. Anyone sophisticated in electronics knows that to process video-even in a digital format-you need to pump the circuits harder, you need faster clocking and you need amplifiers-all features that wind down the battery sooner. Start adding audio, video and data services, and getting more than 15 minutes of battery life out of a cell phone will be the dominant power-management issue for this year and next.

In their exclusive online article for this week's In Focus (www.eet.com/in_focus/), National Semiconductor's Jim Doyle, senior member of the technical staff, and Bill Broach, design manager, describe cell phones using an analogy to the car. We can continue to eke out small returns in fuel economy with improvements to the cooling system, water pump, generator and electrical-distribution system. Like improvements in voltage regulator efficiency in a mobile phone, these will offer incremental advances year by year and model by model. But massive gains in automotive fuel efficiency won't come without a massive overhaul of the engine and power transmission system-perhaps even a replacement of the shop-worn internal-combustion engine with a hybrid model.

While National has a battery of products designed to efficiently control voltages and currents through different parts of a cell phone/PDA combo, Doyle and Broach point out that the real gains come when the handheld system is redesigned in its entirety with power management as a priority. Consequently, this week's contributors, in print and online, can be categorized according to how much a part of the total system their power-management solution is likely to become.

With some of its portable processors-the StrongARM in particular-Intel Corp. counted the number of clock cycles required to perform certain tasks and assigned priorities for those jobs. The energy consumed by each task (the battery drain) turned out to be a function not only of the voltage (and clock frequency) required but of the number of cycles it took to complete the task. A high-energy, high-priority task need not drain the battery if it was short in duration. Similarly, a low-energy task could prove a drain on battery life if it seemed to go on endlessly.

Extending battery life

This notion is advanced by Andrew Girson, CEO of InHand Electronics (Rockville, Md.), in his contribution. InHand is a developer of reference platforms for handheld PDAs. Among the tools the company markets is a cycle counter software package that plots clock frequency against specific tasks (such as memory transfers) and again against battery life (in hours). As it turns out, data transfer rates between memory locations are relatively insensitive to CPU clock frequency, but running the clock faster would drain the battery faster. The recommendation, clearly, is to preserve battery life by using a slower clock during memory transfers-but this may not be true for all tasks.

Other system-oriented exclusive online contributors look at a means of tailoring portions of a cell phone system to use power more efficiently-ideally, drawing juice only when and if it is needed. Toshiba's Ritch Russ (Raleigh, N.C.) points to lower battery voltages that need less regulation but more closely match the IC requirements. Texas Instruments' Masoud Beheshtiat (Dallas) advocates Coulomb counting rather than voltage-level measurements for smart battery-monitoring systems. And Karl Volk of Maxim Integrated Products (Sunnyvale, Calif.) offers a power circuit for RF devices whose voltage output tracks the power envelope for a CDMA handset transmitter.