Battery-monitoring IC reduces BMS cost by 80% in hybrid and electric vehicles

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 10microseconds. 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 (100microamps, operating mode) to conserve battery life. A unique built-in shutdown feature reduces consumption to an ultra-low 1microamp 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
* 100microamps in operating mode; 1microamp 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 degrees Celsius to +105 degrees Celsius AEC-Q100 Type 2 temperature range. Prices start at $8.12 (100-up, FOB USA).