Battery-pack controller manages 14-cell lithium ion sources to ASIL-C

September 18, 2014 // By Graham Prophet
Freescale's integrated battery cell controller is designed to improve functional safety, robustness and affordability; it balances measurement accuracy, scalability and high speed isolated communications for automotive and industrial battery management

The integrated 14-cell lithium-ion battery cell controller is aimed at industrial and automotive applications, designed to cost effectively meet the stringent requirements for ASIL-C functional safety. With 14 cell balancing transistors, a current sensor with ±0.5% accuracy from milliamps to kiloamps, and 2 Mbps communication transceiver interface integrated into a single 64-pin QFP package, the MC33771 battery cell controller and companion MC33664 isolated communications interface handle 48 V battery systems, enabling economical scalability beyond 1000V.

Built-in diagnostics help protect automotive and industrial battery packs against critical fault conditions, and its transformer-coupled isolated high speed transceiver eliminates the need for expensive isolated CAN buses to meet ASIL-C requirements. Together, these features suit the products to a range of range of automotive and industrial applications including 48V battery packs, hybrid and electric cars, E-bikes and energy storage systems.

A battery cell controller must provide precise and reliable battery diagnostics by accurately measuring differential cell voltages, temperatures and currents. It is equally critical that this information be communicated quickly and accurately from the battery cell controller to the pack controller for system-wide control and safety of the battery, allowing the full energy content of the battery to be utilised. The MC33771 incorporates the capability to synchronously measure currents and voltages with 2 mV accuracy within 65 µsec, making it easier to meet ISO 26262 ASIL-C requirements. Embedded functional verification and fault diagnostics enable compliance with ISO 26262 ASIL-C functional safety standards without additional external circuitry.

For higher voltage systems, the integrated daisy chain differential transceiver communicates at 2 Mbps using transformer coupled isolation up to 3750V, while the MC33664 connects the battery pack directly to the system MCU's dual SPI interface using the same transformer coupled isolation.