ROHM Semiconductor announced that it has developed a wireless power supply IC chipset consisting of the receiver – ML7670 – and transmitter – ML7671 – compatible with Near Field Communication (NFC) technology for compact wearables such as smart rings and smart bands, as well as peripheral devices like smart pens.
The smart ring market has experienced growth in recent years, primarily in healthcare and fitness applications. However, for extremely small ring-shaped devices worn on the finger, wired charging is impractical, while the conventional Qi wireless charging standard is difficult to implement due to constraints such as coil size. This has resulted in increased demand for a proximity-based power transfer method capable of charging ultra-compact devices.
In response, NFC-based charging, which operates at the high-frequency 13.56 MHz band that enables antenna miniaturization, is gaining adoption in next-generation wearables. Following the commercial release of the 1 W ML7660/ML7661, ROHM has developed the ML7670/ML7671 chipset optimized for smaller devices.
This new chipset is based on the receiver – ML7660 – and transmitter – ML7661. The maximum power transfer is specified at 250 mW, while peripheral components such as the switching MOSFETs required to supply power to the charging IC are built in. The result is a solution designed for reduced mounting area and specified power transfer efficiency in the power class demanded by compact wearable devices, especially smart rings.
The ML7670 power receiver IC achieves a maximum power transfer efficiency of 45% in the 250-mW low-output range all in a specified form factor of just 2.28 × 2.56 × 0.48 mm. A key feature of the new chipset is reported efficiency compared to similar products in the same class by optimizing elements such as coil matching, rectifier circuitry, and reduced losses in switching devices.
Additionally, all firmware required for wireless power delivery is embedded directly within the IC, eliminating the need for a host MCU. This reduces board space along with the development workload in device design.
Compliance with NFC Forum (WLC 2.0) enables power transfer while maintaining compatibility with existing devices, allowing use within the NFC wireless power ecosystem.
The new chipset is already in mass production. Furthermore, it has been adopted in SOXAI RING 2, the latest model launched on December 10, 2025, by SOXAI, Inc. (“SOXAI” is pronounced “SOK-sai”), the Japanese developer and distributor of the sleep monitoring ring SOXAI RING. Evaluation boards and reference designs are also available for integration.
The SOXAI RING is a smart ring developed in Japan for sleep monitoring and health tracking. It integrates an optical vital sensor, temperature sensor, accelerometer, Bluetooth® Low Energy connectivity, and NFC wireless charging. The latest SOXAI RING 2 model incorporates Deep Sensing™, a proprietary photoplethysmography (PPG) sensor technology that improves measurement accuracy and enables more detailed health monitoring.
Going forward, ROHM Semiconductor plans to continue developing compact, low-power devices for wearable applications such as smart rings, smart bands, smart pens, wireless earphones, and other portable electronics.