Innovative Wireless Charging for Wearable Devices Based on STWLC38

Wireless charging is rapidly emerging as a transformative technology, with electromagnetic induction and resonant charging being the most prevalent methods. The Wireless Power Consortium (WPC) maintains standards for various wireless charging applications, including the Qi standard, which supports up to 15W charging for smartphones and portable devices. As a leading semiconductor company, STMicroelectronics (ST) is a key contributor to this evolving field.

STMicroelectronics STWLC38 and Wireless Charging

STMicroelectronics stands at the forefront of innovation, offering advanced wireless charging solutions across consumer electronics, medical, and industrial applications. Wireless charging enhances device durability by enabling waterproof and dustproof designs, improves user convenience, and eliminates the need for physical charging ports. Beyond battery charging, wireless power transfer (WPT) also supports direct power delivery in industrial and medical applications, facilitating greater mobility for robotic arms and ensuring sealed, sterilizable designs for medical devices.

STWLC38: Optimized Wireless Charging for Compact Devices

ST provides wireless charging solutions ranging from 1W to 100W. The STWLC38 is a Qi 1.3-certified wireless power receiver optimized for space-constrained devices such as wearables and earbuds. It delivers up to 15W of power while maintaining a compact total footprint of just 7mm x 7mm, including peripheral components. The STWLC38 is designed to operate seamlessly with the STWBC86 transmitter chip.

Housed in a 2.1mm x 3.3mm WLCSP40 package, the STWLC38 supports an adjustable output voltage from 4V to 12V with a 25mV resolution. It integrates an ARM 32-bit Cortex-M0+ processor running at up to 64MHz, along with 64kB ROM, 16kB RAM, and 32kB RRAM, which allows firmware patches similar to flash memory.

Advanced Features for Enhanced Performance

One critical aspect of wireless charging design is foreign object detection (FOD). The STWLC38 precisely measures voltage and current to identify foreign metallic objects, preventing potential overheating by automatically cutting off power. Additionally, the receiver includes comprehensive protections against overcurrent, overvoltage, and overheating.

The STWBC86 transmitter chip complements the STWLC38, offering compatibility with the Qi 1.2.4 standard and a maximum transmission power of 5W. It integrates a full-bridge inverter and features a 64MHz ARM Cortex-M0+ processor with 8kB RAM and 8kB FTP for firmware updates. Optimized for Qi standard A11a topology, the STWBC86 employs low-resistance inverters for improved efficiency.

Turnkey Solutions for Streamlined Development

Transitioning from wired to wireless charging presents a significant challenge for developers. To simplify this process, ST provides ready-to-use solutions:

• STDES-WLC38WA & STDES-WBC86TX: A complete wearable wireless charging solution, including PCB Gerber files, firmware, software, design guidelines, and technical documentation. With a compact 7mm x 7mm PCB footprint, this solution is ideal for space-constrained applications.

• STDES-WLC38TWS: A proven TWS (True Wireless Stereo) charging case solution with an optimized custom coil, allowing developers to create wireless charging solutions effortlessly.

Superior Efficiency and Adaptive Technology

The STWLC38 offers outstanding efficiency within the 5W to 15W power range. To address misalignment issues between transmitters and receivers, ST has introduced Adaptive Rectifier Configuration (ARC) technology. ARC ensures reliable charging even with up to 50% misalignment, significantly enhancing user experience by eliminating the need for precise coil alignment.

Additionally, ST’s receiver ICs enable reverse wireless charging, allowing a device with an ST receiver chip to function as a wireless transmitter. This feature supports scenarios where a smartphone can charge a smartwatch or another mobile device wirelessly.

Qi Pre-Compliance and Accelerated CertificationSTDES-WLC38TWS

Achieving Qi certification can be time-consuming and costly. To support developers, ST provides pre-compliance testing solutions, enabling faster prototyping and a smoother certification process. By leveraging ST’s technology, innovators can accelerate product development and ensure seamless interoperability with Qi-compliant wireless chargers.

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Conclusion

STMicroelectronics’ STWLC38-based wireless charging solution offers a breakthrough for wearable devices, providing a compact, high-efficiency, and feature-rich platform. With advanced FOD protection, ARC technology, reverse charging capability, and streamlined Qi certification, ST enables faster development cycles and enhanced user experiences. As wireless charging continues to evolve, ST’s innovative solutions will play a pivotal role in shaping the future of consumer electronics and industrial applications.

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