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Linear debuts monitor ICs to drive hybrids, cars

Posted: 25 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:hybrid? electric car? Li-ion battery?

Linear Technology Corp. introduces its first monitoring chips that can help in producing long-awaited electric cars, hybrids and other systems based on Li-ion batteries.

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

The device responds to several problems in Li-ion design, such as the ability to produce a reliable, long-lasting battery stack. Li-ion is expected to be the next battery for hybrids, electric cars and other systems.

The next top choice
In the future, most hybrid cars are anticipated to shift toward Li-ion batteries. Toyota's third-generation hybrid cars, due this late 2008 or early 2009, are cited to use Li-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.

Li-ion is said to provide twice the energy density of NiMH, which is the battery technology used in today's hybrid vehicles. But Li-ion cells are sensitive to overcharging or over-discharging. "This as a result can create a thermal runaway condition, or worse catastrophic failure," said Linear.

"The problem with Li-ion batteries is that you can't cycle the battery over the various temperature ranges,'' said Erik Soule, VP and general manager, signal conditioning products, Linear.

Responding to the needs
With its new device, Linear claimed it has addressed an issue for Li-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 added.

Hybrids make up only 2 percent of the cars sold worldwide today, making this an attractive market for Linear and other chipmakers. Linear is no stranger to the automotive segment, where it gets its 10 percent total sales.

"We were very early in producing chips for hybrids," he noted. 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.

Chip features
Based on a 0.6? BiCMOS process technology, the device is said to be a complete battery monitoring IC. It consists of a 12bit delta sigma ADC, a precision voltage reference, an input multiplexor and serial interface.

In systems like hybrids and electric cars, multiple LI-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 believed 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 13ms. Each device in a string communicates via 1MHz serial interface. 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 -40C to 85C.

The chip comes in a 44-lead SSOP package. The chip is manufactured within Linear's 6-inch fab near its headquarters in Milpitas, California.

- Mark LaPedus
EE Times

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