STMicroelectronics has expanded its STM32U3 ultra-low-power microcontroller family with the STM32U3B5 and STM32U3C5, two new Arm Cortex-M33 MCUs that pack up to 640 KB SRAM and 2 MB flash memory. The standout addition is a hardware signal processor (HSP) accelerator designed to run AI and machine learning workloads using only energy harvesting, eliminating the need for batteries in certain applications. Both chips maintain the 96 MHz clock speed of their predecessors and operate down to 0.65V thanks to near-threshold design, delivering 117 CoreMark/mW in active mode and functioning in ambient temperatures up to 105°C (221°F).
The new MCUs beef up connectivity with four SPI and I2C interfaces, two I3C and CAN-FD ports, and five UARTs, along with 10 16-bit timers compared to five in earlier models. The STM32U3C5 adds a cryptocore for hardware-accelerated encryption and decryption, plus support for the Coupling and Chaining Bridge (CCB) security feature, both absent from the STM32U3B5. According to STMicroelectronics, the HSP accelerator delivers 13x better performance than a standard Cortex-M33, 9x better power efficiency than an STM32U5, and up to 9x better performance than a Cortex-M33 running TensorFlow Lite for tasks like keyword spotting and image classification.
The STM32U3 series received support in Zephyr RTOS starting in June 2025, with I2C support added shortly after as part of the ongoing collaboration between STMicroelectronics and the open-source community. Developers can use standard open-source toolchains including arm-none-eabi-gcc and OpenOCD for programming and debugging, with STMicroelectronics maintaining its own OpenOCD fork with extended STM32 support. Alternative firmware libraries like libopencm3 provide additional open-source development options alongside ST's official HAL drivers.
Power consumption ranges from 1.6 μA in Stop 3 mode with 8 KB SRAM to 20 μA/MHz at 96 MHz in active mode. The chips come in nine package options from a compact 3.67 x 3.58 mm (0.14 x 0.14 inches) WLCSP up to a 20 x 20 mm (0.79 x 0.79 inches) LQFP144, all ECOPACK2 compliant. STMicroelectronics plans to demonstrate a batteryless setup at Embedded World 2026 using the NUCLEO-U3C5ZI-Q development board with an STM32U3C5 and camera powered by photovoltaic modules running person detection via the HSP.
The entry-level STM32U3B5CG in 48-pin packages costs $2.93 (€2.70) per unit for 10,000-piece orders, while the top-end 144-pin STM32U3C5ZI runs $4.68 (€4.30) per unit at the same volume. The NUCLEO-U3C5ZI-Q development board is listed at $30 (€28) on Future Electronics. Software support includes the STM32CubeMX code generator, STM32CubeU3 MCU package, and the STM32 AI software ecosystem for AI development.
