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Battery-monitoring IC suits hybrid vehicles

Maxim Integrated Products introduces the MAX11068, a high voltage, 12 cell, battery-monitoring IC for hybrid vehicles, electric vehicles, and any system that stacks long series strings of batteries. This highly integrated solution employs a proprietary SMBus-laddered communication bus that allows multiple MAX11068s to be daisy-chained together without expensive isolators. This approach reduces battery-management system (BMS) cost by up to 80%, while simplifying battery pack design and precisely balancing cells for maximum energy delivery.

Offering excellent accuracy, ultra-low power consumption, built-in safety and diagnostic features, and plenty of configurability, the MAX11068 solves the problems associated with safely monitoring large battery stacks and accurately balancing cells. It is well suited for a wide spectrum of battery applications including automotive, industrial, power line, and battery backup.

Lithium-ion (Li+) batteries are expected to dominate the market by 2015, as they offer higher energy densities and, therefore, longer per-charge driving ranges than nickel-metal hydride (NiMH) batteries. Yet, Li+ batteries are particularly volatile, requiring careful design and sophisticated monitoring schemes to ensure safe operation. Cell overvoltages can cause a rapid increase in cell temperature, producing a thermal-runaway condition where cells can catch fire. Since HEVs often require hundreds of cells in series, the consequences of such a failure are substantial: A fault in one cell could cause the entire battery pack to burn or explode.

Today's battery pack designers invest a tremendous amount of time to ensure the absolute safety of their stacks. Advanced safety analysis methods like FMEA and ISO 26262 are deployed to ensure that the state of the battery is well known. The present circuits are bulky and costly, not to mention less reliable than an integrated solution.

The MAX11068 greatly simplifies the design of high-cell-count battery packs. A 12-cell measurement system, this device employs a capacitor-isolated SMBus-laddered communication bus to minimize component count and cost. This unique architecture allows up to 31 devices to be connected in a series stack to monitor as many as 372 cells. The capacitor-based interface provides extremely low-cost isolation from one bank of batteries to the next, eliminating cascading electrical failures.

The MAX11068's analog front-end combines a 12-channel voltage-measurement data-acquisition system with a high-voltage, fault-tolerant switch bank input. A high-speed, 12-bit ADC is used to digitize the cell voltages. The MAX11068 employs a two-phase scanning approach to collect cell measurements and correct them for errors. This technique delivers cell-measurement simultaneity, allowing all cell-measurement samples of a 120-cell pack to be co-sited within 10 microseconds. This ensures high accuracy in the face of extreme system noise. The MAX11068 delivers less than ± 0.25% error over normal battery temperature ranges and ± 20 mV error over the full AEC-Q100 Type 2 temperature range.

The MAX11068 can be paired with the MAX11080 redundant fault monitor to deliver a complete 12-cell solution. Designed to facilitate the transition to carbon-neutral energy solutions, this line of high-voltage devices integrates sophisticated functions to reduce the size, cost, and complexity of battery-management systems. Users will benefit from enhanced reliability, longer battery life, and accelerated time to market.

The MAX11068 is packaged in a 38-pin TSSOP and is fully specified for operation over the -40° to 105° C AEC-Q100 Type 2 temperature range.

For more information, contact Maxim Integrated Products, 120 San Gabriel Dr., Sunnyvale, CA 94086. Phone: (408) 737-7600.

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