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ST Debuts Wireless MCU for LoRa

February 18, 2020

Author: Tom R. Halfhill

Anyone who recharges a smartphone daily would envy a wireless communicator that could run for a decade on a coin-size battery. It’s possible with LoRa (Long Range), a low-power wide-area-network (LPWAN) technology. The catch is that LoRa is designed for brief bursts of low-bandwidth data instead of high-bandwidth voice and data. But its nine-mile range and extremely low power make it ideal for remote sensors and meters in IoT applications. To drive down the cost of LoRa and similar LPWANs, STMicroelectronics is shipping the industry’s first microcontroller with a fully integrated LoRa radio.

The new STM32WLE5 is a 32-bit Arm-based MCU containing ST’s custom implementation of a Semtech SX126x LoRa-compliant radio that operates in the unlicensed sub-GHz radio-frequency bands. Its RF coverage of 150–960MHz ensures compatibility in North America and Australia (915MHz), Europe (433MHz and 868MHz), and Asia (923MHz). These bands have better obstacle penetration than higher-frequency Wi-Fi and cellular bands, but power constraints limit their range in hilly terrain, cities, office buildings, and factories. LoRa can also track mobile objects (such as shipping containers) using radio triangulation instead of power-hungry satellite geolocation.

Three STM32LE5 models join the extensive STM32 family, which includes larger STM32WB MCUs that operate in the 2.4GHz bands. Like those parts, the new chips have Arm Cortex-M4 CPUs, but they run at 48MHz instead of 64MHz and omit several features, such as the LCD, USB, touchscreen, and digital-audio interfaces.

Other MCUs require a separate RF transceiver or a dual-die package, which is costlier, more power hungry, and slower to waken from sleep mode. ST says the STM32WLE5 is so flexible that one board design can work in all global regions. The chips are in production now and start at less than $3 in volume.

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