"The basic issue is that the density of the power we are dealing with [in laptops] is quite hazardous," said Dean McCarron, an analyst at Mercury Research (Cave Creek, Ariz.).

"We've created a beast," said Jim Templeton, co-founder of power-management IC startup Zilker Labs Inc. (Austin, Texas). "Notebooks have rising thermal envelopes, more localized hot spots and limited cost budgets to solve these rising power-management challenges."

Engineers, testers and other industry experts said last week that quality control problems at battery maker Sony's production lines, along with a lack of robust battery cell materials, were key contributors to the largest consumer recall in history. But design engineers said the proliferation of smaller, graphics-intensive mobile devices is raising more-fundamental issues.

"It's a matter of how systems are architected," said Bodo Arlt, publisher of Bodo's Power Systems magazine in Germany. "You need to know how much energy the computer extracts from the battery, and how a system is designed to manage the current flow that generates heat inside the battery. Knowing the limitation at the critical temperature is important."

Added Arlt, "Graphics-intensive applications such as computer games could create a huge stress on computers, resulting in a demand for extreme power. Once [a computer] overheats, it can start burning."

Overtemperature circuitry
Robert Dobkin, CTO and vice president of engineering at Linear Technology Corp., said it's a mistake to focus on the placement of battery packs relative to microprocessors and graphics processors on a laptop motherboard. Overtemperature circuitry prevents today's battery packs from charging at temperatures greater than 45°C to 50°C, Dobkin said. In his view, the overheating from processor power dissipation could lead to system problems, but not the catastrophic fires seen in some laptop failures.

Instead, fire danger relates to battery chemistry in poorly designed batteries, or in the overvoltage protection used in integrated battery packs, he said. Simple Li-ion designs lack the ability to handle overvoltage, Dobkin said, so the battery manufacturer or system OEMs must add it. Sony and other large battery makers integrate a voltage protector into the pack, he said.

McCarron of Mercury Research said most consumers don't realize how much power is packed into lithium-ion batteries--a notebook battery can hold as much as 100 watt-hours of energy--and how sensitive the chemistry is to disruptions.

In this case, he said, Dell may have been guilty of design flaws that created hot spots within the notebook case. But McCarron said the recall stemmed from quality control problems at Sony.

A testing lab official agreed. "It is basically a quality [control] problem in the cells," said John Drengenberg, an electrical engineer and manager of consumer affairs for Underwriter Laboratories Inc. (Northbrook, Ill.). "Power density is increasing dramatically," he added, while battery cell materials have failed to keep pace.

Reports last week suggested that faulty crimping on a Sony production line may have introduced metal contamination to the cathodes of the affected battery packs, leading to a half-dozen or more reported fires. "If it were a design problem at Dell, we would have had many more [fire] problems," said McCarron.

A Sony spokesman in Tokyo said, "Our analysis thus far shows that a tiny metal particle that contaminated the electrolyte inside the battery cell caused a short-circuit." But he added, "Usually, that alone would not cause a fire, because the battery just goes dead at that point. We believe the fire was caused by the combination of batteries and [PC] system architecture."

Dell is not alone in its purchase of Sony lithium-ion batteries produced between January 2004 and February 2006--the period when it is believed the metal contamination may have occurred. Other companies' notebooks, including Sony's own Vaio computers, use the same type of batteries manufactured during this period, but only Dell has issued a recall.

Li-ion batteries require a very precise charger that prevents charging above 4.1 volts. The choice of such chargers rests with the laptop OEM, not the battery manufacturer. LTC's Dobkin said suppliers do not provide precision chargers to Dell, so the problem can reside either in legitimate semiconductors that do not meet spec or in counterfeit parts that have problems with grounding pads or poor packages.

The impact of counterfeit components may be larger than the industry wants to admit, according to an article by Michael Pecht and Sanjay Tiku in the May issue of IEEE Spectrum. Pecht, the founder and director of the Center for Advanced Life Cycle Engineering at the University of Maryland, said the complex layers of outsourcing of the supply chain make it next to impossible to point fingers in product recalls. "There is such a concern with reducing the overall price in consumer goods these days [that] companies have turned to levels of outsourcing where accountability is very tough," Pecht said. Power subsystems also can fall victim to counterfeit chips or passive components. "Any component is a potential target," he said.

Intel Corp. is leading an effort to reduce the overall power consumption in notebooks, which can have a thermal upper limit of 70 W. As more functions are packed into notebooks, ranging from wireless components to high-transistor-count graphics chips that burn hot while videogames or movies are displayed, it's getting harder to keep them cool. The Intel-led the Narrow VDC (voltage, direct current) initiative is striving to reduce the overall power consumption. But while a few OEMs have adopted the Narrow VDC approach, it is far from widespread.

Rick Doherty, an analyst at The Envisioneering Group (Seaford, N.Y.), maintained that many Dell designs place the battery toward the front, closer to the CPU and graphics processor. Thus, "parts of the battery get hotter [than others]. ... So the six to 10 cells that are within the battery pack don't stay matched during thermal stress," he said. Notebooks from Apple, Sony and others tend to put the battery in the back of the system, Doherty said.

Anne Camden, a spokeswoman at Dell's mobile-systems unit, challenged that assertion, saying that various Dell notebooks have the batteries in different positions, depending on system model. "And I can assure you, our engineers design these systems with the utmost attention to thermal and safety issues," she said.

Smarter silicon
Some industry watchers last week called for more intelligent silicon as a way to improve the safety of mobile systems. But others pointed out that some silicon solutions may be too expensive for cost-conscious consumer manufacturers. Digital power management can do much to improve product safety, throttling down when batteries run into problems. But "we are scraping the bottom" in terms of squeezing costs out of notebooks, making the conversion to more-expensive silicon difficult, said Templeton of Zilker Labs.

For example, servers and networking equipment may benefit from digitally enhanced power regulators, which use DSPs and supporting logic to precisely regulate the multiple voltage rails used in today's complex systems. But those chips may come slowly to notebooks.

Patrick Heyer, a systems engineer at the battery-management products unit at Texas Instruments Inc., said TI has introduced new design techniques for ICs used within the battery packs (the so-called gas gauge products) as well as for the battery-charging ICs. In a typical notebook, these power ICs are tied to a microcontroller, which also regulates the keyboard. TI has developed gas gauge chips and battery chargers that communicate over the SMBus, improving safety margins, he said.

This week, TI will introduce second-generation ICs that track the impedance (resistance) within the battery pack, giving notebook designers a new tool in the effort to "gain some better understanding of what the state of the battery is," Heyer said.

-- Additional reporting by Spencer Chin, George Leopold and Junko Yoshida