NXP Rolls out MCUs Aimed at Traction Inverter Control in EVs

We kick off our coverage of the Electronica trade fair today with NXP Semiconductors’ announcement of its latest electric vehicle (EV)-focused microcontroller. The Electronica trade faiir runs November 15-19 here in Munich, Germany. We’re pleased to be walking the halls of the show here with our EETech team.

Today, NXP has launched its S32K39 Series MCUs for EVs. Specifically, the series addresses the complex set of requirements for modern EV designs.

All About Circuits Editor-in-Chief Jeff Child at NXP’s booth at Electronica talking with NXP’s Brian Carlson about the company’s new S32K39 MCUs.

In this article, we discuss the issues that the S32K39 solves for EV designs, examine the details of the device, and share insights from our interview with Brian Carlson, NXP’s Director, Global Product and Solutions Marketing, Automotive Processing – Vehicle Control and Networking Solutions.

Three Key Requirements for New EV Designs

According to Carlson, the S32K39 addresses three key issues in modern EV design. First, it meets the needs of new EV traction inverter control needs. This entails blending performance, integration, networking, security and functional safety. Second, the MCUs support remote smart actuation applications using Time-Sensitive Networking (TSN) Ethernet for new zonal vehicle architectures. And finally, the device shrinks system cost by providing ASIL D software resolver and analog integration.

In an EV, the traction inverter subsystem plays a central role in an EV. The electric motor controls the speeding up and stopping of the vehicle, and must work in conjunction with the brakes. All the intelligence to do that comes together in the EV’s traction inverter.

As Carlson explains, the traction inverter is where the S32K39 serves as the “brains.” With this in mind, the device offers several features that directly focus on issues surrounding the traction inverter. These are illustrated in the diagram below.

The S32K39 MCU was crafted to meet EV design needs that revolve around an EV’s traction inverter subsystem. Image used courtesy of NXP

Increasing driving range is a fundamental goal in EV design. How much efficiency you can get out of a battery is part of the equation. Meanwhile, every bit of integration that reduces overall weight translates to more driving range. High functional safety with ASIL D is also critical, especially as cars add more autonomy.

Being able to scale up the number of motors is a key trend in today’s designs. An entry-level EV may use a single motor, while a mid-level sedan or SUV may want to add performance and go to dual motors. Another trend is increasing motor phases from 3-phase motors to 6-phase. The S32K39 supports these multiple motor designs and 6- or 3-phase motor options.

TSN Ethernet and High-speed Switching

Importantly, the S32K39 supports, not just Ethernet, but Time Sensitive Networking (TSN) Ethernet. This enables support for zonal remote smart actuation. “Through TSN, I can actually drive a motor directly,” says Carlson. The S32K39s can do the motor control and link to one of NXP’s S32E2 controllers to function as the overall EV controller and do the power conversion.

In this EV design, an S32K39 is the brains of a “smart” actuator doing dual motor control, while an S32E2 does the overall EV propulsion control. Image used courtesy of NXP

The high-performance processing capabilities of the S32K39 translates into faster switching speeds, says Carlson. The S32K39 can do two 200 kHx control loops in parallel. That will accommodate the new high-speed switching technologies for gate drivers and switches that are emerging. “Those are typically in the 10 kHz range today, but they will go up to 200 kHz as new technologies like SiC (silicon carbide) and gallium nitride (GaN) come into play,” says Carlson.

Carlson says that capabilities such as those are examples of why MCUs like the S32K39 are not devices that are adapted from MCUs made for internal combustion engine cars, but rather are MCUs designed specifically for modern EVs.

Details of the S32K39 MCU Architecture

Looking now at the details of the S32K39 device, at the heart of the MCU are a set of Arm Cortex M7 CPU cores running at 320 MHz. Those are supplemented by an integrated NXP CoolFlux DSP block.

Carlson says the DSP enables designers to get rid of the need for external components for doing the resolver and filtering functions. Moreover, with the DSP integrated, engineers can do custom filters. That means they can do more advanced algorithms and they can improve them over time.

“They're not just relying on what a vendor gives them—a hard version of something,” says Carlson. “They have flexibility to customize for their applications. That offload some of the performance that's needed also. And it reduces cost because it removes an external part that would have been needed to provide that feature.”

Block diagram of the S32K39 MCU. Image used courtesy of NXP. (Click image to enlarge)

Another key piece of the MCU is its set of two motor control coprocessors. The complete EV motor could be run on each of these—the Motor Control Core A and Motor Control Core B. In fact, the processor could be spread out anyway the designer wishes. Calson says this enables flexibility.

“We give customers flexibility because some do some processing on the Arm processors, some of them do it on the coprocessors, or on  combination of those. It gives them the freedom to optimize their solutions. It's all about that flexibility.”

Rich On-chip Analog Resources

In terms of the chip’s analog block, the MCU has sigma-delta analog-to-digital converters (ADCs), which are important for high-resolution for the resolver functionality. The MCU also features up to 7 SAR ADCs, enabling 69 SAR ADCs channels. There are also 12 channels of high-resolution PWM (pulse width modulation) and dual analog comparators.

The S32K39 boasts an embedded Hardware Security Engine (HSE_B). Carlson says this allows the device to do trusted execution on boot (secure boot). Full encryption is provided for public key infrastructure (PKI), which is used for over the air (OTA) firmware updates.

Gearing up for New Complex EV Challenges

There’s no doubt that designing today’s new EVs is a complex engineering challenge. Cars based on internal combustion engines are inherently linked to mechanical and chemical processes that are evolutionary. In contrast, EVs are essentially one big set of complex electronic circuitry, which means they can leverage advances in embedded electronics faster and at a whole different scale. It could be said that solutions like NXP’s new S32K39 MCU series represent a vivid example of that trend.