Wireless battery management systems highlight drive for higher reliability

Greg Zimmer, Sr. Product Marketing Engineer, Signal Conditioning Products, Linear Technology Corporation -November 25, 2016

Lithium-Ion batteries require considerable care if they are expected to operate reliably over a long period.  They cannot be operated to the extreme end of their state of charge (SOC).  The capacity of lithium ion cells diminishes and diverges over time and usage, so every cell in a system must be managed to keep it within a constrained SOC.

To provide sufficient power for a vehicle, tens or hundreds of battery cells are required, configured in a long series generating as much as 1000V or higher.  The battery electronics must operate at this very high voltage and reject common mode voltage effects, while differentially measuring and controlling each cell in these strings. The electronics must be able to communicate information from each cell in a battery stack to a central point for processing.

In addition, operating a high voltage battery stack in a vehicle or other high-power applications imposes tough conditions, such as operation with significant electrical noise and wide operating temperatures.  The battery management electronics are expected to maximize operating range, lifetime, safety, and reliability, while minimizing cost, size, and weight.

Steady advances in Linear Technology’s battery cell monitoring ICs have enabled high performance, increased life, and reliability of battery packs in automobiles today. Wireless battery management systems (BMS) promise to further improve safety and reliability of the full battery system.

Battery monitoring

In 2008, Linear Technology announced the first high performance multicell battery stack monitor, the LTC6802. Among its key features, the LTC6802 measures up to 12 Li-Ion cells with 0.25% maximum total measurement error within 13ms, and many LTC6802 ICs can be connected in series to enable the simultaneous cell monitoring of every cell of a long, high voltage battery strings. Linear Technology has improved upon the LTC6802 many times over the years.  All of the devices in Linear’s LTC68XX family are intended for precision battery management within hybrid/electric vehicle (HEVs), electric vehicles (EVs) and other high voltage, high power battery stacks.

Each LTC6811 includes two built-in 1MHz serial interfaces, an SPI interface for connecting to a local microprocessor, and the proprietary 2-wire isoSPI interface.  The isoSPI interface provides two communication options: multiple devices can be connected in a daisy chain to the BMS master (host processor) or multiple devices can be connected and addressed in parallel to the BMS master.

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