Date: 06/08/2010

Power IC for electric vehicles cuts battery-management system's cost from $250 to $50

Maxim introduces the MAX11068, a high-voltage, 12-cell, battery-monitoring IC for hybrid vehicles, electric vehicles, and any system that stacks long strings of individual batteries. This chip by using SMBus-laddered communication bus allows multiple MAX11068s to be daisy chained together without isolators. Maxim claims 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 and consumes 75% less space than discrete designs. Maxim claims solution based in this chip can reduce the expense of a typical battery-management system from $250 to a mere $50.

Maxim says 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.

Release states 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.

Specs and features: 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.

MAX11068 consumes100µA of current in operating mode and has built-in shutdown feature with 1µA leakage current, allowing the pack to be stored for many years without draining the battery.

The MAX11068 is designed to withstand harsh magnetic fields and transient noise typically normal in automotives.