David Carey, President, Portelligent
TechOnline

Portable power management is arguably at its zenith in the cell phone. Handset owners expect incredible battery life in their phones and designers try to deliver by conserving coulombs when and wherever possible. All in all, the industry has worked wonders here, providing hours of talk time and days of standby from batteries whose capacity rarely exceeds a few watt-hours.

But restless consumers drive the addition of new features, often with little room for increased cost or shorter battery life. The application-specific standard product (ASSP) has been the industry's general solution to providing more for less. These highly integrated building blocks serve a range of cell phone functions and, unlike custom devices, are widely available to all.

One company with a history of merchant-market ASSP use, Research in Motion (RIM), has had a stellar run with the Blackberry family, and the latest 8700, Figure 1, handheld seems to be on track to continue the success.

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Figure 1: The RIM 8700 Blackberry from Research in Motion provdes email support and a full QWERTY keyboard.
Still centered on push e-mail, the 8700 provides a generous screen and small QWERTY keyboard to keep the loyal following heads downs and thumbs up.

The inside view of the 8700 provides a view of the significant switch for RIM to Intel's applications/cellu-lar multicore processor for system logic. Figure 2.

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Figure 2: Power-management ICs and algorithms are key to the design's efficiency.
With integration as the theme, RIM has lashed the PXA901 "Hermone" processor and stacked memory to a multichip radio package from RFMD. Similarly, the multiband RF power amplifier combines a mix of chips and discretes in a single package to reduce apparent complexity. A single Maxim component serves audio needs in the design, save for a small external audio power amplifier from the same company.

Each of these big blocks-integrated though they may be-still has an individually challenging power supply design, such that multiple isolated supplies must be created at the system level. As one of the first in the category of comprehensive cell phone power-management units that are not proprietary ASICs, TI's TPS65800 was chosen for RIM's design. It combines several DC/DC regulators and a half-dozen low-dropout (LDO) supplies in a device that also manages battery charging. Ultimately, the 8700 made use of several other external LDO parts, but the TI component keeps much of the power-management circus under one tent.

Power supply design in mobiles gets pretty hairy past the battery terminals. Even there, the delicate job of managing charge/discharge cycles can challenge. By latching onto a high-volume market with well-defined needs, these thorny tasks can be tackled in an analog ASSP that is both affordable to the customer and profitable for the maker. Integration rules, and mobile power management is no exception.

About the author
David Carey is president of Portelligent, www.teardown.com. The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics.