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Linear’s IC to enable hybrids, electric cars

SAN JOSE, Calif. — Analog specialist Linear Technology Corp. today is expected to roll out the first in a family of monitoring chips that could help enable long-awaited electric cars, hybrids and other systems based on lithium-ion batteries.

Linear's LTC6802 is an integrated device that can measure and monitor the precise voltage levels for up to 12 individual lithium-ion cells in electric and hybrid cars. Other applications for the device include boats, golf carts, motorcycles, portable equipment, power supplies, wheelchairs and other products.

The device solves several major problems in lithium-ion design, including the ability to develop a reliable, long-lasting battery stack. Lithium-ion is supposedly the next battery of choice for hybrids and electric cars and other systems.

Most–if not–all hybrid cars in the future will move towards lithium-ion batteries. For example, Toyota's third-generation hybrid cars, due out in late 2008 or early 2009, will use lithium-ion batteries, according to the Japanese car giant. Electric cars from General Motors and a plethora of startups are also expected to use the technology.

Lithium-ion is said to provide twice the energy density of nickel-metal hydride (NiMH), which is the battery technology used in today's hybrid vehicles. But lithium-ion cells are sensitive to overcharging or over-discharging. This in turn could create a ''thermal runaway condition,'' or worse, ''catastrophic failure,'' according to Linear.

The problem with lithium-ion batteries is that “you can't cycle the battery over the various temperature ranges,'' said Erik Soule, vice president and general manager of Signal Conditioning Products at Linear (Milpitas, Calif.).

With its new device, Linear believes it has addressed at least one issue for lithium-ion batteries, especially for the booming hybrid and electric automotive market. The overall automotive business is flat to down, but ''the growth for hybrids is very significant,” he said.

Hybrids make up only 2 percent of the cars sold in the world today, making this an attractive market for Linear and other chip makers. In fact, Linear is no stranger to the automotive segment; in total, it derives some 10 percent of its sales in the arena.

“We were very early [in developing] chips for hybrids,'' he said. Previously, Linear sold analog-based discrete components in this market. What's different is that the new LTC6802 is the company's first integrated ASSP for the sector.

Based on a 0.6-micron BiCMOS process technology, the device is said to be a complete battery monitoring IC. It consists of a 12-bit delta sigma analog-to-digital converter, a precision voltage reference, an input multiplexor and serial interface.

In systems like hybrids and electric cars, multiple lithium-ion batteries are connected in a string. But any single cell failure will disable the entire stack.

Therefore, each cell must be monitored and controlled. The LTC6802 from Linear is said to make that possible ” even in the presence of stacked voltages over 1000V. Multiple LTC6802 devices can be stacked in a series of cells without the need for optocouplers or isolators, according to Linear.

All cell voltages in a battery stack can be measured within 13-ms. Each device in a string communicates via a 1-MHz serial interface. And each cell is monitored for under-voltage and over-voltage conditions. An associated MOSFET switch is available to discharge overcharged cells. The maximum total measurement error is guaranteed at less than 0.25 percent from minus 40 degrees Celsius to 85 degrees Celsius.

The chip is priced at $9.95 each in 1,000-piece lots. It comes in a 44-lead SSOP package. The chip is manufactured within Linear's 6-inch fab near its headquarters in Milpitas.

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