In conventional systems, a complicated algorithm running remotely on a high-end microcontroller decides which cells have to be balanced. The new architecture supported by the AS8506 can control balancing locally at the cells, enabling designers to implement a more streamlined cell management system that eliminates the powerful host controller, complex software and vulnerable serial communication links normally used today.

The AS8506 can implement both passive and active cell balancing autonomously, or it can support a microcontroller-based system via its Serial Peripheral Interface.

An advanced analog circuit in the AS8506 compares up to seven cell voltages against an internal or external reference with an accuracy of 1mV, to support cell-balancing and cell-monitoring functions. Cell voltage measurements can also be digitized with an accuracy of 5mV and reported to a host controller.

Active and passive cell balancing use a similar circuit design, but active balancing requires an additional flyback transformer. The control circuit is integrated in the AS8506.

The device also features internally or external adjustable upper and lower cell voltage limits. Temperature measurement is carried out through two external NTC sensors.

The fully autonomous cell management architecture enabled by the AS8506 is in contrast to the typical system implementations found today using existing cell monitoring ICs. These are typically limited to the sequential capturing of cell voltage measurements that must be processed by a host controller. These prior architectures have several drawbacks for designers of battery management systems, according to ams:

• The system must stream large amounts of data over a serial link—a communications channel that is vulnerable to interference in noisy environments.

• A powerful host controller running complex software is required to turn individual cell voltage measurements into useful functions such cell balancing decisions. Writing this software is a difficult and time-consuming task. The software requires exhaustive testing in order to qualify for use in automotive ISO26262-compliant systems.

• Sequential cell measurements require complex compensation algorithms in order to produce valid voltage and current readings across a stack of cells. By contrast, the simultaneous measurements captured by the AS8506 require no compensation.

The AS8506 marks a breakthrough in cell monitoring—not an incremental improvement on previous cell monitoring ICs, but a completely new approach. By offering local cell and temperature monitoring, the AS8506 gives system designers a simple and robust means to implement a battery management system, with just a simple microcontroller required for basic system functions.

—Manfred Brandl, Product Manager for battery management in the automotive business unit at ams

ams is demonstrating the AS8506 at the VDI Congress on “Elektronik im Kraftfahrzeug” (“Vehicle Electronics”) in Baden-Baden, Germany, 16-17 October 2013.

The AS8506 cell monitoring IC is available for sampling now. It is priced at $9.10 for 1,000 pieces. ams also provides a non-automotive version called the AS8506C. It is priced at $7.80 for 1,000 pieces.