Low-power MCUs offer advanced cybersecurity

Low-power MCUs offer advanced cybersecurity

Technology News |
By Jean-Pierre Joosting

STMicroelectronics has announced a new generation of extreme power-saving microcontrollers (MCUs), the STM32U5 series, to meet the most demanding power/performance requirements for smart applications including wearables, personal medical devices, home automation, and industrial sensors.

STM32 MCUs are built upon the highly energy-efficient Arm® Cortex®-M processors, are already in billions of domestic appliances, industrial controls, computer peripherals, communication devices, and equipment managing smart cities and infrastructure.

The latest STM32U5 series teams the efficient Arm Cortex-M33 core with ST’s innovative proprietary power-saving features and on-chip IP cutting down energy demand while pumping up performance. The line also adds new state-of-the-art features needed by today’s applications, including advanced cybersecurity with new hardware-based protection targeting PSA and SESIP (Security Evaluation Standard for IoT Platforms) assurance level 3, as well as graphics accelerators for rich user experiences.

ST has also created the STM32U5 IoT Discovery Kit (B-U585I-IOT02A)  that combines the MCU with a Wi-Fi® module, Bluetooth® module, and various sensors. Microsoft has chosen this kit as reference board for the new Azure Certified Device program. “The STM32U5 provides an excellent platform for delivering Azure IoT services via Azure RTOS leveraging the advanced features of STM32U5 microcontroller,” said Sam George, Corporate Vice President, Azure IoT at Microsoft Corporation. The kit will be available to order later in the year.

Low power design

The microcontrollers introduce an innovative autonomous mode that lets direct memory access (DMA) and peripherals keep working while most of the device sleeps, to save power. Granular control over operating modes allows part of the MCU’s memory to be turned off, to avoid powering unused cells. In addition, STM32U5 MCUs are manufactured using 40nm process geometry, the most advanced node suitable for MCUs, which saves power in dynamic operating modes as well as power-saving modes.

There are also proven features from the preceding STM32L0, STM32L4, and STM32L5 ultra-low-power MCUs. These include dynamic voltage scaling, which optimizes energy consumption according to the workload, and the ST ART Accelerator™ to read Flash memory efficiently. An update to the ST ART Accelerator now allows reading of off-chip Flash as well as the MCU’s internal memory.

By Integrating an advanced DC/DC converter and low-dropout (LDO) regulator, connected in parallel and selectable on-the-fly, STM32U5 MCUs can cut dynamic power consumption to less than 19µA/MHz.

“ST has almost doubled its share of global microcontroller sales in the last five years, shipping more than two billion ultra-low-power STM32 devices to date. With our low-power expertise and focus, we are particularly strong in the ultra-low-power category with about 25% of that market,” said Ricardo de Sa Earp, Group Vice President, Microcontroller Division General Manager, STMicroelectronics. “We expect our STM32U5 microcontrollers to be even more popular, enabling our customers to create new smart consumer and industrial products that deliver superior energy rating, performance, and cyberprotection.”

Advanced peripherals

In addition to saving power, designers can tackle demanding applications leveraging new features such as greater Flash density. The first STM32U5s will have 786 KB of RAM and up to 2 MB of Flash. This includes 512 KB of high endurance cells capable of 100,000 read-write cycles. Developers can use this longer-lasting memory for user data to create products with a drastically longer life span.

An advanced high-speed 14-bit analog-to-digital converter (ADC) is provided, ready for next-generation sensing and tracking applications. The ADC is capable of 2.5 mega samples per second or an 18-bit mode that offers even greater accuracy. It also provides a math accelerator (FMAC and CORDIC) to optimize motor control and digital power applications. Engineers can even envision running simple user interfaces thanks to the ChromART Accelerator™ and the presence of advanced display interfaces.

A Multi-function Digital Filter (MDF) and Audio Digital Filter (ADF) upgrade the capabilities of the company’s proven Digital Filter for Sigma-Delta Modulator (DFSDM). By boosting performance in sound-activity detection, these now enable users to infuse AI into low-cost, low-power microcontroller-based use cases. Moreover, with Error Correction Code (ECC) memory as part of the device’s RAM, STM32U5 MCUs can also fulfil safety-centric applications.

Focus on security

Building on the cybersecurity focus of the STM32L5, which includes a Cortex-M33 core with Arm TrustZone® technology and an ST-specific security feature set, the STM32U5 series introduces new and state-of-the-art innovations, including:

  • AES encryption and Public Key Authorization (PKA) are now hardware resistant to side-channel attacks by Differential Power Analysis (DPA);
  • Secure data storage with a Hardware Unique Key (HUK);
  • Active tamper detection;
  • Internal monitoring that can erase secret data in the event of perturbation attacks helps meet the PCI Security Standards Council (PCI SSC) requirements for Point Of Sales (POS) applications.

“Today’s smart applications need to be power efficient and built on a secure foundation,” said Mohamed Awad, vice president, IoT Business, Arm. “ST has incorporated Arm technology into its latest MCUs, taking energy efficiency and security to the next level, while developers can also utilize the Arm Keil® MDK for ultimate energy optimization.”


Among lead customers for the STM32U5, Twilio, the leading cloud communications platform, has used the MCUs to create an innovative IoT device-builder platform called Microvisor. Jonathan Williams, Lead Product Manager at Twilio, commented, “Being among the first developers to start using the STM32U5 has given Twilio Microvisor that unique combination of extreme low power, efficient performance, and advanced cybersecurity that Twilio customers are asking for.”

Up till now, teams working on IoT systems must either design everything from scratch or remain subject to an entire ecosystem. There are pros and cons to both approaches. Microvisor offers a new middle ground that uses byte code that lives in the TrustZone of the STM32U5 to take care of security and connectivity. Teams that want to tweak their system can do so. Microvisor is flexible enough to allow developers to use their operating system and drivers. Similarly, developers with few resources bypass tremendous challenges to obtain a highly secure environment. Relying on TrustZone enables Microvisor to implement security features, such as Secure Boot, or Secure Firmware Over-the-Air Updates.


Azure RTOS will be integrated in the STM32Cube software suite, with configuration features in STM32CubeMX and STM32CubeIDE tools and addition of examples, bringing additional key benefits to STM32Cube such as fast performance and industry certifications.

The B-U585I-IOT02A Discovery Kit will enable a wide diversity of applications by exploiting low-power communication, multiway sensing and direct connection to cloud servers. It includes Wi-Fi and Bluetooth modules, as well as microphones, temperature and humidity, magnetometer, accelerometer and gyroscope, pressure, Time-of-Flight and gesture-detection sensors.

STM32U5 MCUs are sampling now to lead customers and will be in full production in September 2021. Budgetary pricing starts at $3.60. A broad choice of packages including a 4.2-mm x 3.95-mm WLCSP and 7-mm x 7-mm UQFN48 and UFBGA169 will be available.

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