ST is launching the STM32U0, the first Cortex-M0+ with a static consumption of 160 nA in standby mode with RTC (Real-Time Clock) and 16 nA in shutdown. It also offers 140 points in CoreMark and SESIP level 3 capabilities, making it one of the most capable MCUs in the ultra-low power entry-level segment. This is possible because the STM32U0 adopts many features we’ve been implementing in other devices while reusing a 90-nm process node that offers exceptional yields. Consequently, the STM32U0 achieves one of the best static consumption at this price point, granting engineers more freedom to optimize their design for entry-level battery-powered applications in industrial, medical, smart metering, and consumer wellness markets.
The power effectiveness of the STM32U0
Demos in action
One of the STM32U0 demos that garnered a lot of attention is an illuminometer built using Dracula Technologies photovoltaic module. It runs on a small photovoltaic panel instead of a traditional battery. It can fully operate down to 5 lux (corresponding to a very dark room) because of the low static power consumption in the STOP 2 mode of the STM32U0 and the efficient active mode. Indeed, as the illuminometer spends most of its time in a low-power state waiting to be awoken, the new efficiency of the STM32U0 opens the door to applications with a much smaller power source.
Similarly, another ST customer replaced the MCU in their water metering system with an STM32U0 and noticed a 38% drop in the overall power consumption. Even better, we have measurements showing a 50% gain in energy saving when using the STM32U0 to manage sensors in industrial applications. Put simply, the increase in efficiency is noticeable and opens the door to entirely new applications.
The low power modes in numbers
The STM32U0 comes with many low-power modes, granting developers more flexibility. For instance, STOP2 with RTC needs 630 nA, while supporting full memory retention. Hence, developers must mostly figure out the acceptable wake-up time for their application and then choose the lowest power consumption that suits their needs. There are also other low-power modes, like a 30 nA Standby mode that needs only six pins for the wake-up process.
The features
Lowering the bill of materials
Traditionally, STM32 series ending with a “0” target entry-level applications. Hence, the STM32U0 aims to bring more features to cost-constrained systems. For instance, the new device includes a multi-speed internal (MSI) RC oscillator. As a result, the system no longer requires a high-frequency crystal, enabling HSI (high-speed internal) accuracy within +/- 1%. Additionally, it is possible to auto-calibrate the MSI with a low-speed external crystal (LSE) at 32.768 kHz. This is what we call PLL mode, and it allows for the same accuracy as the LSE crystal. Hence, besides lowering the bill of materials, it also simplifies the PCB design since the STM32U0s can auto-calibrate.
A resourceful architecture
To make this entry-level device even more compelling, ST maximized the number of integrated peripherals. We include a segment display controller, so engineers don’t have to add an external one. Similarly, very few competing devices offer digital-to-analog and analog-to-digital converters, an operational amplifier, and an ultra-low power comparator. Consequently, developers can provide new features to their users that they weren’t originally going to offer, or they can ship the same features at a lower price, making their product more accessible.
If we take a step back, the features of the STM32U0 show why this is a device inspired by the STM32L0, STM32L4, and STM32U5. The new model includes five 16-bit timers, one 32-bit timer, three ultra-low-power timers, up to three ultra-low-power UART interfaces, and up to two ultra-low-power comparators. Its touch-sensing controller also makes it easy to add a basic button to improve user interactions. The new ultra-low-power MCU also includes ST’s Adaptive Real-Time (ART) Accelerator, which fetches instructions faster by preemptively loading them into a cache directly available to the Cortex core. This optimization further helps save energy by enabling more instructions per clock cycle.
Another feature we are bringing to entry-level applications is the VBAT mode, which can automatically power-switch the Real Time Clock (RTC) and backup registers to a backup battery when the main power supply goes down. The STM32U0 with 256 KB of flash also includes a USB device crystal-less solution, meaning that the controller is included on the die and doesn’t require an external oscillator to work.
Comprehensive security
The STM32U0 is the first MCUs with an Arm® Cortex®-M0+ targeting SESIP Level 3 and PSA level 1 focusing on firmware code protection. Certification provides independent assurance of the device’s security capabilities. Product manufacturers need to leverage them to comply with coming voluntary US Cyber Trust Mark and mandatory EU Radio Equipment Directive (RED). Furthermore, the STM32U0 offers a true number generator and an AES 128/256 accelerator. It is rare to see such a strong focus on security on an entry-level device, but it reflects a desire to make secure embedded systems more accessible to all designs by ensuring that even cost-effective systems can enjoy them.
The cost-effectiveness
Lowering costs
The STM32U0s will start at 68 cents for 1,000 units. Hence, despite all these features and capabilities, we still managed to keep the price below a dollar. In addition, the STM32U0 offers significant energy savings, thus extending the product life cycle and enabling customers to use and smaller and more cost-effective battery without sacrificing battery life. Additionally, integrators get many integrated peripherals that are responsible for lowering the overall BOM.
Benefitting from the STM32 ecosystem
Another important metric is that the STM32U0s are pin-to-pin compatible with the STM32L0s, L1s, and L4s. In a nutshell, it’s possible to more easily port code written for an STM32L MCU to the new STM32U0, which vastly saves on development costs and reduces the time to market. In a nutshell, the STM32U0 will help teams save energy and provide the optimal compromise between energy consumption, integrated features, and cost-effectiveness.
