ROHM launches an Ultra-Compact Wireless Power Chipset for Wearables

ROHM 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 seen rapid 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 conventional Qi wireless charging standard is difficult to implement due to constraints such as coil size. This has driven increased demand for a proximity-based power transfer method capable of reliably charging ultra-compact devices.

In response, NFC-based charging, which operates at the high-frequency 13.56MHz band that enables antenna miniaturization, is attracting increased attention, with adoption accelerating in next-generation wearables. Following the successful commercialization of the 1W ML7660/ML7661, ROHM has developed the ML7670/ML7671 chipset optimized for even smaller devices.

This new chipset builds on the proven receiver – ML7660 –  and transmitter – ML7661. The maximum power transfer is specified at 250mW, while peripheral components such as the switching MOSFETs required to supply power to the charging IC are built in. The result is a solution optimized for both mounting area and power transfer efficiency in the power class demanded by compact wearable devices, especially smart rings.

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The ML7670 power receiver IC achieves a maximum power transfer efficiency of 45% in the 250mW low output range – all in an industry-leading form factor of just 2.28 × 2.56 × 0.48mm. A key feature of the new chipset is superior performance that surpasses the efficiency of comparable products in the same class by optimizing elements such as coil matching, rectifier circuitry, and reduced losses in switching devices.

What’s more, all firmware required for wireless power delivery is embedded directly within the IC, eliminating the need for a host MCU. This significantly reduces board space along with development workload in device design.

Compliance with NFC Forum (WLC 2.0) enables power transfer while maintaining compatibility with existing devices, positioning the chipset as a core element in the expanding 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 original sleep monitoring ring SOXAI RING. Evaluation boards and reference designs are also offered to facilitate integration. For more information, please contact a sales representative or submit an inquiry via the contact page on ROHM’s website.

Going forward, ROHM will continue to promote device development that leverages miniaturization and low-power consumption technologies essential for wearable devices, contributing to improved user convenience and the continued growth of the wearable market.

Specifications

(Fig. 3)

Case Study: SOXAI RING 2 Adoption Example
SOXAI RING is the only smart ring for sleep management developed in Japan capable of accurately capturing and analyzing sleep data. It incorporates cutting-edge technologies such as an optical vital sensor, temperature sensor, accelerometer, Bluetooth^® Low Energy communication, and NFC wireless charging functionality.
The latest model, SOXAI RING 2, is equipped with Deep Sensing™, a proprietary photoplethysmography (PPG) sensor that significantly improves measurement accuracy, enabling the visualization of physical health changes with far greater depth and precision. (Fig. 4)

Bluetooth^® is a registered trademark of Bluetooth SIG, Inc. in the US.
Deep Sensing™ is a trademark or registered trademark of SOXAI, Inc.

Application Examples
• Smart rings
• Smart bands
• Smart pens
• Wireless earphones
• Other compact devices (i.e., wearables)

Terminology
NFC Forum
An international standards organization for contactless communication that defines communication and wireless power transfer methods based on Near Field Communication (NFC), a short-range wireless communication technology operating in the 13.56MHz high-frequency band.

Qi Standard
An international standard for wireless power transfer developed by the Wireless Power Consortium. Often adopted for wirelessly charging smartphones.

Credit: ROHM