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New IC reduces battery-management system costs by 80 percent in hybrid and electric vehicles

August 06, 2010 | Paul Buckley | 222901003
New IC reduces battery-management system costs by 80 percent in hybrid and electric vehicles Maxim Integrated Products has introduced a high-voltage, 12-cell, battery-monitoring IC for hybrid vehicles, electric vehicles, and any system that stacks long series strings of batteries.
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The integrated solution employs a proprietary SMBus-laddered communication bus that allows multiple MAX11068s to be daisy chained together without expensive isolators. The approach reduces battery-management system (BMS) cost by up to 80 percent, while simplifying battery pack design and precisely balancing cells for maximum energy delivery.

Claiming world-class 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.

The fuel tank of the future, HEV battery packs are a critical part of the drive train for next-generation transportation systems.

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 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 aims to simplify 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. The 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 low-cost isolation from one bank of batteries to the next, eliminating cascading electrical failures.

Maxim's solution consumes 75 percent less space than discrete designs. Altogether, it can reduce the expense of a typical battery-management system from 250 US Dollars to 50 US Dollars.

Beyond cost savings, Maxim's solution claims to deliver unparalleled performance. Maxim's high-voltage, small-geometry BiCMOS process enables the industry's highest voltage tolerance (80 V), excellent ESD performance (±2 kV, Human Body Model), hot-plug capability, and reliable AEC-Q100-compliant performance over a wide temperature range.

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. The technique delivers cell-measurement simultaneity, allowing all cell-measurement samples of a 120-cell pack to be co-sited within 10microseconds. This ensures accuracy in the face of extreme system noise. The MAX11068 delivers less than ±0.25 percent error over normal battery temperature ranges and ±20mV error over the full AEC-Q100 Type 2 temperature range.

Additionally, the MAX11068 offers a 10x reduction in power consumption (100 microamps, operating mode) to conserve battery life. A built-in shutdown feature reduces consumption to an ultra-low 1 microamp leakage, allowing the pack to be stored for many years without draining the battery.

The MAX11068 has built-in configuration and self-diagnostic modes, which are crucial for safely monitoring system operation. It delivers faultless operation in the face of harsh magnetic fields and transient noise. Maxim extensively tests the IC using bulk-current-injection, stripline, and in-vehicle testing to ensure glitch-free operation when subjected to the large electrical transients and magnetic fields produced in high-power electric vehicle battery packs. The device has been designed to handle open- and shorted-pin detection and internal block faulty operation per FMEA standards.

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. Customers will benefit from enhanced reliability, longer battery life, and accelerated time to market.

Summary of MAX11068 features

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