ANAHEIM, Calif. Texas Instruments Inc. will use the Power2001 conference Monday (Oct. 1) to introduce two battery-management systems for new-generation rechargeable batteries. One is designed for fuel gauging and charge control in larger systems employing embedded lithium-ion batteries; the other is designed to cut the power dissipation and component count in handheld portables such as cell phones, personal digital assistants (PDAs) and MP3 players.
The annual conference, sponsored by Arthur D. Little consultants and mounted by the Giga Information Group, is a showcase for new battery chemistries and form factors as well as their power-management electronics. New portable applications will demand new flexible form factors, said Rob Enderle, Giga's research fellow, who will deliver a "visionary" keynote at the conference, which runs through Oct. 3.
"Battery technology has been running fairly slow," Enderle said. It is more likely we'll see dramatic new form factors in the near term, rather than adoption of new chemistries like lithium-polymer. As computers themselves will change form factors, becoming more portable, more attached to us like cell phones, the batteries will change form, he said. And as computers become wearable, there will be an increased need to minimize heat dissipation. "Computing products that generate heat will be harder to get into your pocket," he said.
The challenge for battery-management electronics is to preserve power when portable computers are responding to an "always-on" and "always-connected" demand pattern. Enderle foresees devices that absorb broadcast power or respond to energy in the environment, like the Pico Radios explored by the Wireless Research Center at the University of California, Berkeley.
TI's smart-battery IC introductions are meant to capture the trend toward totally embedded rechargeable batteries begun with the Mitsubishi Pedion laptop, said David Heacock, TI's business manager for battery-management products. Because the battery cannot be replaced by simply removing it from its host, extra care must be utilized to preserve battery life not to stress the battery on either its charge or discharge cycles.
For handheld devices like cell phones, the peak current consumption (which will depend on the cell phone's distance from the basestation) is about 1 amp, while the average current consumption is 150 to 600 milliamps, Heacock said. Notebook computers, on the other hand, can consume about 45 watts at full tilt. The power consumption for PDAs is more modest: about 1 watt for a monochrome unit; 6 W for a color device. But consumer add-ons, such as Bluetooth or 802.11 wireless modems and music playback units, will tax battery life. The embedded voltage regulator must be better than 92 percent efficient to prevent heat dissipation, Heacock said.
TI's solutions one for handhelds, another for portable computers are specifically intended to provide a high degree of charging control and high efficiency, yet avoid stresses on potentially embedded batteries. The single-chip bq2420x family is intended for PDAs and handhelds. It includes a current sensor and an internal MOSFET pass transistor, rated for up to 500-mA charge applications.
The bq2420x actually answers a controversy over what to do when the available Li-Ion battery cell voltage ordinarily at 3.6 V at full charge drops below the 3.3 V required to power portable logic. Some argue the cell phone should be turned off when the available battery voltage drops below 3.5 V, and that linear step-down regulators would likely provide the required regulation. Others argue that a switching regulator with a buck-boost topology can squeeze out extra battery life (like a toothpaste dispenser) by lifting the drooping battery voltage to the required logic level. Switching regulators, moreover, have the advantage of high efficiency.
The efficiency of switching regulators is high when current demands are high but tends to drop when the load is low, Heacock said. A low-dropout linear regulator can be as efficient as switchers with 150-mA loads, and attempting to boost the voltage of a nearly spent 3.6-V battery will only add stress something which will tax the life of an embedded cell.
The other system TI will introduce which includes the bq2081 Smart Battery System Gas Gauge IC and the bq29311 Li-Ion Protector IC is meant for higher-current systems like portable computers. The chip set can reduce the number of components required for a Li-Ion smart-battery-system (SBS)-compatible battery fuel gauge and protection circuit by as much as 40 percent, Heacock said. The platform integrates an 8-bit RISC CPU core, flash EPROM configuration memory, two communication ports, safety control outputs and two high-performance analog-to-digital converters. It is fully compliant with the Smart Battery Specification version 1.1.
Up in the air
"More than 60 percent of portable computers are using the smart-battery technology," said Brian Fritz, applications engineer with Maxim Integrated Products (Sunnyvale, Calif.), who was scheduled to give a talk on version 2.0 of the SMBus at the conference. "And about half of those use the Smart Battery Spec in a straightforward manner," he said.
Maxim had helped Intel and Duracell draft the original smart-battery specification. It has four elements, Fritz said. One is a physical-layer specification. The two-wire SMBus is very much like I2C, except that it includes voltage levels and status indicators for hot-plugging. Another part of the Smart Battery Spec is what Fritz calls a "data spec," which describes the mechanism for transferring commands and information between the smart battery and its computer host. There is also a smart-battery charging spec and in the new version a smart-battery manager spec for systems with multiple batteries, he said.
"No one knows where the new spec is going," Fritz cautioned. "It's a little up in the air." Maxim's own smart-battery products include the MAX1780 smart-battery controller, and the MAX1645A SMBus charge controller, complaint with version 1.1 of the Smart Battery Spec.
PowerSmart Inc. (Shelton, Conn.), the IC maker spun out from Duracell's Smart Battery thrusts, recently introduced the PS401 Accuron, an SBS-compliant battery-management IC. The device integrates all monitoring functions on a single chip, minimizing the parts count and costs.
The Accuron combines a proprietary RISC microcontroller with 12 kbytes of EPROM and 128 x 8 bytes of E2PROM for program and data storage. The analog front end includes a 15-bit digital-to-analog converter that keeps reporting errors of charge and run-time below 1 percent, which is important for accurate fuel gauging and for maximizing battery life.