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Get an edge: Battery Management

Electric vehicle designers rely on Maxim for battery products that extend driving range, optimize control, and guarantee safety. Maxim's high-voltage process technologies, coupled with nearly two decades of battery management expertise, enable advanced charging and protection solutions capable of robust operation in the face of system noise.

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 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.

Power lithium-ion technologies-an explosive market
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.

The challenge: bringing down the cost of safety
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 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. Maxim's solution consumes 75% less space than discrete designs. Altogether, it can reduce the expense of a typical battery-management system from $250 to a mere $50.

The MAX11068 sets new performance benchmarks
Beyond cost savings, Maxim's solution delivers unparalleled performance. Maxim's high-voltage, small-geometry BiCMOS process enables the industry's highest voltage tolerance (80V), excellent ESD performance (±2kV, 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. This technique delivers cell-measurement simultaneity, allowing all cell-measurement samples of a 120-cell pack to be co-sited within 10µs. This ensures excellent accuracy in the face of extreme system noise. The MAX11068 delivers less than ±0.25% 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 (100µA, operating mode) to conserve battery life. A unique built-in shutdown feature reduces consumption to an ultra-low 1µA leakage, allowing the pack to be stored for many years without draining the battery.

Designed for automotive
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.

Maxim's family enables clean energy applications
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

2-cell to 12-cell Li+ battery measurement
Capacitor-isolated daisy-chain interface
Eliminates costly isolation components
Allows up to 31 MAX11068s to be connected in series for as many as 372 cells
Rugged, fault-tolerant design offers high noise immunity
Fully programmable via simple I²C/SMBus-laddered serial bus
±0.25% cell-measurement error
Two temperature channels
Single board design supports packs with various cell counts
Built-in diagnostics
Ultra-low power consumption
100µA in operating mode; 1µA in shutdown mode
Operates from 6V to 72V; withstands transients up to 80V
Available stripline and bulk-current-injection performance metrics
The MAX11068 is packaged in a 38-pin TSSOP and is fully specified for operation over the -40°C to +105°C AEC-Q100 Type 2 temperature range. Prices start at $8.12 (100-up, FOB USA).

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