Battery-protection IC reduces hybrid car battery-management system costs by 80 percent

Battery-protection IC reduces hybrid car battery-management system costs by 80 percent

A high-voltage, 12-channel battery-protection IC for high-cell-count lithium-ion (Li+) battery stacks has been introduced by Maxim Integrated Products.

Claimed to be the first stackable fault monitor on the market, the MAX11080 provides redundant cell monitoring to prevent Li+ batteries from exploding (thermal runaway). Up to 31 MAX11080s can be daisy-chained together to monitor as many as 372 cells. The capability prevents cascading electrical failures and eliminates the isolation components required by discrete solutions. In a typical hybrid car, Maxim's solution claims to reduce the cost of the battery-management system (BMS) by up to 80 percent.

Offering world-class accuracy, ultra-low power consumption, built-in safety and self-diagnostic features, and plenty of configurability, the MAX11080 solves the problems associated with safely monitoring large battery stacks. The solution is well suited for a spectrum of battery applications including automotive, industrial, power line, and battery backup.

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

Though nickel-metal hydride (NiMH) was the battery chemistry of choice in the first HEVs, Li+ batteries are expected to dominate the market by 2015, as they offer a higher energy density and, therefore, longer per-charge driving range. Lux Research predicts that Li+ battery sales will jump from $6.8 billion in 2007 sales to $16.9 billion in 2012.

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 in which gases are vented. Since HEVs often require hundreds of cells in series, the consequences of a failure are substantial: a fault in one cell could cause the entire battery pack to burn or explode.

Battery pack designers are tasked with ensuring the safety of their stacks. Typical protection circuits employ multiple 3- or 4-channel fault monitors with galvanic isolators between the monitors and an assortment of analog and passive components (resistors, multiplexers). These circuits are bulky, costly and time intensive.

The MAX11080 simplifies the design of high-cell-count battery packs. A 12-channel fault monitor, this device employs a proprietary capacitor-isolated daisy-chain interface 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. Meanwhile, the capacitor-based interface provides extremely low-cost isolation from one bank of batteries to the next, eliminating cascading electrical failures.

Dispatching of the need for isolation components, 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 to a mere $50.

The company'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-swap capability, and reliable performance over a wide temperature range. To protect against battery thermal runaway, the MAX11080's accurate overvoltage detection guarantees less than ±25 mV error over the full AEC-Q100 Type 2 temperature range (-40 to +105 degrees Celsius).

Additionally, the MAX11080 offers a 10x reduction in power consumption (80 microamps, operating mode) to conserve battery life. A built-in shutdown feature reduces consumption to an ultra-low 2 microamp leakage, allowing the pack to be stored for many years with very little battery drain.

The MAX11080 has 16 selectable overvoltage thresholds, as well as 8 selectable undervoltage thresholds. The undervoltage-detection feature can be disabled if desired. The device includes a programmable detection-delay feature that allows the user to filter out transient events in the battery pack to eliminate false overvoltage or undervoltage alarms. The alarm line operates using a 4 kHz heartbeat signal, the absence of which indicates a valid overvoltage or undervoltage event. These features are critical for discriminating between legitimate and false alarms, preventing the application from shutting down unnecessarily.

The MAX11080 has built-in self-configuration and self-diagnostic modes. On power-up the device automatically detects the presence of batteries and can be configured from 2 to 12 cells in any connection sequence or installation pattern. The device also self tests the internal comparator circuitry to ensure proper functionality on power-up. It is capable of detecting the open or short of any pin on the package and constantly monitors the pins for such a failure.

Packaging and Pricing

The MAX11080 is packaged in a 38-pin TSSOP and is fully specified for operation over the -40 to +105 degrees Celsius temperature range.

Prices start at $3.92 (100-up, FOB USA).

Datasheet for: MAX11080