STM32L431KBU6 ST Mainstream Arm Cortex-M4 Ultra-Low-Power 32-bit MCU 128KB Flash 64KB SRAM USB ADC DAC Comparator UFQFPN-32

STM32L431KBU6 Product Overview

STM32L431KBU6 is an Arm Cortex-M4 MCU at 80 MHz with FPU and ART Accelerator, UFQFPN-32. 128 KB Flash, 64 KB SRAM, USB 2.0 FS device (crystal-less), 12-bit ADC (10 ch), two 12-bit DACs, two comparators, LP timers, RTC, 2×USART, 1×UART, 1×LPUART, 2×SPI/I2S, 2×I2C. Up to 26 x 5 V-tolerant I/Os. 1.71–3.6 V, -40–85 °C. Compared to the LQFP-48 STM32L431CBT6, the STM32L431KBU6 adopts a more compact 32-pin QFN package, significantly reducing PCB footprint while retaining all core peripherals and the same 64 KB SRAM, making it ideal for extremely space-constrained, battery-powered IoT nodes, portable devices, and sensor applications.

STM32L431KBU6 Core Features

Core: The STM32L431KBU6 features an Arm Cortex-M4 core at 80 MHz, with FPU + ART Accelerator

Memory: The STM32L431KBU6 provides 128 KB Flash and 64 KB SRAM (incl. 16 KB with HW parity), offering a balanced combination for embedded applications

USB: The STM32L431KBU6 integrates a USB 2.0 FS device (crystal-less)

Analog: 12-bit ADC (10 ch), 2×12-bit DACs, 2×Comparators

Connectivity: 2×USART, 1×UART, 1×LPUART, 2×SPI/I2S, 2×I2C

Timers: 1×Advanced Timer, multiple GP/LP timers, RTC

I/Os: 26 (5 V-tolerant)

Package: UFQFPN-32

Temperature Range: -40°C to 85°C

STM32L431KBU6 Applications

IoT Sensor Nodes: Battery-powered wireless sensors and USB data acquisition modules can leverage the STM32L431KBU6's low power and compact size

Portable Devices: Wearables, portable medical devices, and USB peripherals benefit from the STM32L431KBU6's ultra-compact integration

Industrial Metering: Water, gas, and electricity meters are ideal applications for the STM32L431KBU6

Consumer Electronics: Remote controls, e-labels, smart cards

Extremely Space-Constrained Low-Power Applications: Miniaturized controllers and energy harvesting nodes can rely on the STM32L431KBU6

STM32L431KBU6 Key Advantages

Cortex-M4 + FPU + Ultra-Low Power: The STM32L431KBU6 delivers excellent DSP and floating-point performance while maintaining extremely low power consumption

Integrated Crystal-less USB: The STM32L431KBU6 enables USB communication without an external crystal, simplifying design and saving BOM

128 KB Flash + 64 KB SRAM: The STM32L431KBU6 provides ample storage for complex programs and data processing

Dual DACs + Dual Comparators: The STM32L431KBU6 offers flexible analog output and signal threshold detection without external components

LPUART Low-Power Serial Interface: Supports asynchronous communication in low-power modes, further optimizing system power consumption

Ultra-Compact UFQFPN-32 Package: Extremely small footprint while retaining all core peripherals, saving PCB space

5 V-tolerant I/Os: Enhanced system noise immunity, simplified external level-shifting circuitry

Full Ecosystem Compatibility: Easy development with STM32CubeIDE/HAL/LL libraries for the STM32L431KBU6

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FAQ

1. What is STM32L431KBU6?
STM32L431KBU6 is an ultra-low-power 32-bit MCU from STMicroelectronics' STM32L4 series, based on an Arm® Cortex®-M4 core with FPU and DSP in a UFQFPN-32 package (5 mm × 5 mm). Running at 80 MHz, the STM32L431KBU6 provides 128 KB Flash and 64 KB SRAM, along with USB OTG FS, high-precision analog peripherals, and extensive low-power modes—delivering an excellent processing platform for space- and power-constrained general-purpose battery-powered devices in an extremely compact footprint.

2. What are the key specifications of STM32L431KBU6?

• Core: Arm® Cortex®-M4, up to 80 MHz, 100 DMIPS with FPU and DSP

• Memory: 128 KB Flash, 64 KB SRAM

• Operating Voltage: 1.71 V to 3.6 V

• Temperature Range: -40 °C to +85 °C (industrial grade)

• I/O Count: up to 26

• Package: UFQFPN-32 (5 mm × 5 mm)

3. What are the characteristics of the UFQFPN-32 package on the STM32L431KBU6? Is it suitable for low-volume hand soldering?
The UFQFPN-32 is an ultra-thin QFN package measuring only 5 mm × 5 mm with an exposed thermal pad underneath. All pins of the STM32L431KBU6 are on the bottom side, so reflow soldering or a hot-air station is required—manual soldering with an iron is not feasible. This package minimizes PCB area but demands precise stencil design and controlled reflow profiles, making the STM32L431KBU6 best for automated SMT production. For prototyping, use a QFN adapter board or the compatible NUCLEO development board for initial validation.

4. What applications is STM32L431KBU6 suitable for?
Thanks to its tiny 32-pin package, 128 KB Flash, USB interface, and outstanding power efficiency, the STM32L431KBU6 is ideal for small battery-powered devices with moderate code size and stringent space/power constraints. Typical applications include portable medical accessories, wireless sensor nodes, miniature USB dongles, consumer wearables, and ultra-compact IoT endpoints requiring simple USB connectivity.

5. What development tools support STM32L431KBU6?
ST provides free STM32CubeMX and STM32CubeIDE with the STM32CubeL4 firmware library for the STM32L431KBU6. Debugging and programming use ST-Link debuggers. The NUCLEO-L432KC board (32-pin package) serves as an excellent starting point for early evaluation—though it carries an L432 chip, most peripherals are compatible, enabling straightforward code migration to the STM32L431KBU6 target.

6. What is the power consumption of the STM32L431KBU6 across its low-power modes?

• Temperature Range: -40 °C to +85 °C

• Ultra-low-power modes of the STM32L431KBU6:

  • Shutdown mode: ~33 nA (5 wake-up pins)

  • Standby mode: ~125 nA (5 wake-up pins), ~430 nA with RTC

  • Stop 2 mode: ~1.2 µA, ~1.4 µA with RTC

  • Run mode: ~100 µA/MHz (LDO mode)

7. How does STM32L431KBU6 differ from STM32L432KBU6?
Both share the same 32-pin QFN package and 80 MHz Cortex-M4 core. The key difference lies in the peripherals: the STM32L431KBU6 lacks the SAI audio interface and CAN 2.0B controller but retains USB OTG FS and rich high-precision analog peripherals. If your project does not require digital audio or industrial bus communication, the STM32L431KBU6 offers better cost-effectiveness while maintaining the same excellent low-power performance.

8. What key peripheral interfaces does STM32L431KBU6 offer?

• Communication: I²C, SPI, UART/USART, USB OTG FS

• Analog: 12-bit 5 Msps ADC, 12-bit DAC, ultra-low-power comparators

• Timers: 16-bit and 32-bit general-purpose timers, advanced motor-control timer

• Others: Quad SPI interface, capacitive touch sensing channels

9. How do USB and other GPIOs share pins in the 32-pin STM32L431KBU6? Are there conflicts?
USB OTG FS on the STM32L431KBU6 uses PA12 (D+) and PA11 (D-) and typically also requires VBUS detect and ID pins (often PA9 and PA10), consuming a few I/Os. With only 26 I/Os available in total, enabling USB leaves approximately 20 GPIOs for other peripherals. It is recommended to use STM32CubeMX for pin assignment of the STM32L431KBU6, prioritizing critical peripherals and flexibly remapping alternate functions.

10. What if my project needs CAN or SAI audio? Can STM32L431KBU6 handle that?
The STM32L431KBU6 does not include native CAN or SAI. If these features are essential, consider stepping up to the STM32L432 (with SAI, no CAN) or STM32L433 (with both CAN and SAI). If you must stick with the STM32L431KBU6, you could add an external CAN controller (e.g., MCP2515) via SPI or an external audio codec via I2S/SPI, but this will increase circuit complexity and BOM cost—so it's best to evaluate early in the design phase.