|Freescale MC 33771 controller addresses the needs of 48V Li-ion battery packs. Click to enlarge.|
Some automakers such as Audi (earlier post) are turning to 48V electrical systems as a technical building block for facilitating the integration of new automotive technologies while increasing the power and efficiency of its cars. Freescale Semiconductor has now introduced a highly integrated 14-cell lithium-ion battery cell controller for industrial and automotive applications that cost-effectively addresses the requirements of 48 V Li-ion battery systems.
With fourteen 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, Freescale’s MC33771 battery cell controller and companion MC33664 isolated communications interface deliver robust, reliable performance for 48 V battery systems, and enable economical scalability beyond 1000 volts.
The solution’s 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 busses to meet ASIL-C requirements. Together, these features make the solution suited for a broad range of automotive and industrial applications, Freescale said, including 48 V battery packs, hybrid and electric cars, E-bikes and energy storage systems.
As automotive and industrial batteries are placed under increasing strain by new, mission-critical applications, challenges such as overcharge, overheating and internal short circuit or overload must be controlled in order to help ensure safe operating conditions. Battery cell controllers need to provide precise and reliable battery diagnostics by accurately measuring differential cell voltages, temperatures and currents.
This information needs to 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 utilized.
The robust design and comprehensive integration of our new battery cell controller reflects Freescale’s system-level approach to cost effectively manage battery charging while helping to prevent failures and dangerous conditions. This new battery cell controller leverages Freescale’s automotive heritage and long history of creating reliable, highly integrated, high-performance solutions to reduce the cost of meeting stringent safety requirements.—James Bates, senior vice president and general manager for Freescale’s Analog & Sensors Group
The MC33771 incorporates many functions required for controlling a single 48 V battery pack, including the capability to measure currents and voltages synchronously with 2 millivolts of accuracy within 65 µs, 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.
|Click to enlarge.|
For higher voltage systems, the integrated daisy chain differential transceiver communicates at 2 Mbps using robust transformer coupled isolation up to 3750 volts instead of expensive isolated CAN busses, while the MC33664 connects the battery pack directly to the system MCU’s dual SPI interface using the same transformer coupled isolation.
The MC33771, in combination with Freescale’s MC33664 isolated communication device, supports optimal lifecycles for a variety of battery architectures, including centralized, distributed CAN and distributed daisy chain topologies. The battery cell controller features a high-speed daisy chain communication design that serves as a replacement for expensive isolated CAN busses. The device’s ability to serve as an alternative to CAN-based solutions eliminates the need for local microcontrollers, voltage regulators and isolated CAN layers within the battery, helping to reduce costs and design complexity.
While Freescale’s MC33771 is usable across most known battery topologies, it features a specific feature set to address a typical 48 V LFP Battery with one device that includes fourteen differential voltage measurements, fourteen embedded cell balancing transistors, seven analog inputs for temperature measurement, one embedded current sensor that synchronizes with the cell voltage measurements to allow determination of individual cell impedance, and a coulomb counter for enhanced state of charge determination.
Additional features include:
- 9.6 V ≤ VPWR ≤ 61.6 V Operation, 70 V transient
- SPI or isolated 2 MHz differential communication
- Current sensor with ±0.5% accuracy from milliamps to kiloamps
- 14x differential cell voltage measurement and stack voltage measurement
- Synchronized cell voltage/current measurement
- Coulomb counting
- 7x ADC/GPIO/temperature sensor inputs
- Addressable on initialization
- Onboard 300 mA passive cell balancing
- Low-power modes
- 64-pin QFP package
The MC33771 and MC33664 devices are sampling now. The versions for the industrial market are expected to be in production by Q1 2015 and the versions for the automotive market are planned for production by Q3 2015.