Highly efficient silicon carbide (SiC)-based power modules enable the largest operating range and faster charging in current EVs. Until recently, however, special, fast signal processors were required to drive these SiC power semiconductors. The Stellar E series of MCUs from STMicroelectronics (ST), designed for the next generation of software-defined EVs, have the processing functions for fast control loops already integrated into the chip, so that a microcontroller can now directly control the entire module. This not only simplifies module design, but also reduces costs and simplifies compliance with automotive safety and security standards.
The new MCUs extend ST’s arm-based Stellar range and are designed from the ground up for automotive use. Used as high-performance, centralised domain and zone controllers, the devices in this family simplify automotive electrical architectures for increased performance, flexibility and safety.
Currently, this MCU family includes the Stellar P series for integration and vehicle control and the Stellar G series for body applications. The Stellar family architecture includes multiple Arm Cortex processor cores that provide high performance with lockstep redundancy capability and support real-time hardware virtualisation. All devices in the Stellar family are designed for software updates through secure OTA updates.
“With the new Stellar-E devices, this platform creates the foundation for a new EV value chain,” said Luca Rodeschini, vice president of the Automotive and Discrete Group at STMicroelectronics. Sensing the environment, controlling vehicle dynamics, increasing power conversion efficiency and safely managing high-current power stages are all effectively handled by a single device. The ability to perform secure OTA software updates further gives manufacturers the ability to refine their control strategies to improve the range, performance and energy efficiency of their vehicles.”
High-power applications in electric vehicles, i.e. the OBC unit, the electric powertrain and the various DC/DC converters distributed throughout the vehicle, can be significantly improved in energy efficiency and reliability when implemented with silicon carbide (SiC)-based power transistors and diodes. These improvement possibilities can be maximised when these semiconductors are operated at higher switching frequencies than is possible with conventional silicon power semiconductors.
Typical automotive MCUs on the market today are not capable of processing the charge control algorithms at a rate that can exploit the higher switching frequencies of SiC semiconductors. Rather, additional DSP chips are required specifically for the control loop, which require separate programming and increase not only the component expense but also the complexity of the control modules implemented with traditional MCUs. Additional costs, extra space and higher power consumption are the result.
With the MCUs from ST’s Stellar-E series, automotive-qualified MCUs are now available that can perform fast control loop processing alongside normal control tasks on one and the same chip. This simplifies design and reduces component complexity, facilitating the move to high-efficiency, SiC-based power modules that provide a wider operating range and enable shorter charge times.
These MCUs can drive multiple power converters and are equipped with a fast A/D converter (ADC), a high-precision PWM (pulse width modulation) controller and fast-response protection circuits for this purpose.
Last but not least, the Stellar E-Series supports the leading automotive standards for functional safety (ISO 26262 ASIL-D), security (HSM -) and software interoperability (Autosar 4.3.x) as well as secured OTA updates. However, designing with the Stellar family brings other advantages, such as a comprehensive software development toolchain with a uniform infrastructure for control and actuator functions.
The first product in the Stellar E series is the Stellar SR5E1, optimised for on-board chargers (OBCs) of EVs and general DC-DC converters. The device is currently being sampled for lead customers and is expected to enter volume production in 2023.