AI-driven near-threshold design for low power microcontroller
STMicroelectronics has used near-threshold design to reduce the energy consumption of its latest low power microcontroller series for remote applications.
The STM32U3 microcontrollers are aimed at low power applications such as utility meters, healthcare devices and industrial sensors, adding encryption key protection and in-factory provisioning to meet coming European cyber regulations.
The ARM Cortex-M33 microcontroller family uses a small digital signal swing close to the threshold of the CMOS transistors to minimise dynamic power consumption. This has been a problem to implement as the process technology can vary, hitting the yield of these transistors. ST has used an AI-driven adaptive voltage scaling at wafer level to compensate for process variations in the foundry.
This reduces the dynamic power to 10µA/MHz with a static current of 1.6µA, and gives the latest core running at up to 96MHz a Coremark-per-milliwatt score of 117. This is almost twice the efficiency of ST’s previous STM32U5 series, and five times that of the STM32L4 series.
The STM32U3 also embeds up to 1MB of Flash memory dual-bank and 256kB of SRAM.
This allows the devices to be used with coin cell batteries or ambient solar or thermoelectric source. The STM32U3 MCUs are also used in consumer products such as smart watches, wearables, and hearables.
“Using recent advancements in near-threshold design, the new devices cut dynamic power consumption to the bone, boosting efficiency by a factor of two compared to our previous generation, hence contributing to companies’ sustainability goals,” said Patrick Aidoune, General-Purpose MCU Division General Manager, STMicroelectronics.
The MCUs are designed to confine encryption keys permanently in secure memory using a coupling and chaining bridge (CCB) to eliminating vulnerable fetch operations. This is the first use of this technology in the STM32 MCU family.
Any attestation credentials are provisioned by ST at manufacture before leaving the factory, which strengthens security and simplifies provisioning. All those security mechanisms, in addition to the SESIP3 and PSA Level3 certifiable security assets, such as cryptographic accelerators, TrustZone isolation, random generator, and product lifecycle will contribute and enable ST customers to reach compliance with the upcoming Cyber Resiliance Act (CRA) regulations in Europe.
There are two product lines available, with or without a hardware cryptographic accelerator
“The STM32U3 enables us to bring our hardware for animal health monitors to the next level. The consumption in active mode is extremely low, only a few µA/MHz, which enables us to reduce the energy needed for current data processing algorithms while at the same time adding new features to our products. In addition, its advanced range of low-power modes lets us put the device into deep sleep if no data is processed. The newly implemented STOP3 mode, including its wakeup capabilities, is a neat way to keep power consumption low,” said Manuel Frech, Product Development Engineer at smaXtec.
The STM32U3 series is available in commercial (-40°C to 85°C) and extended industrial (-40°C to 105°C) temperature ranges and is in production now and available from $1.93 for orders of 10,000 pieces.
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