ROHM has developed a wireless power supply IC chipset consisting of the receiver ML7670 and transmitter ML7671, compatible with Near Field Communication (NFC) technology. The chipset targets compact wearables such as smart rings and smart bands, as well as peripheral devices including smart pens.
The smart ring market has grown in healthcare and fitness applications. Wired charging is impractical for small ring-shaped devices worn on the finger, and the conventional Qi wireless charging standard is difficult to implement due to coil size constraints. This has increased demand for proximity-based power transfer methods suitable for ultra-compact devices.
NFC-based charging operates at the 13.56MHz high-frequency band, enabling antenna miniaturization. Following the commercialization of the 1W ML7660/ML7661 chipset, ROHM developed the ML7670/ML7671 for even smaller devices.
Source and analysis: Rohm
The new chipset supports a maximum power transfer of 250mW. It includes built-in switching MOSFETs for supplying power to the charging IC. This configuration is optimized for mounting area and power transfer efficiency in the power class required by compact wearable devices, particularly smart rings.
The ML7670 power receiver IC measures 2.28 × 2.56 × 0.48mm and achieves a maximum power transfer efficiency of 45% in the 250mW range. The chipset optimizes coil matching, rectifier circuitry, and switching device losses to deliver performance that exceeds comparable products in the same class.
All firmware required for wireless power delivery is embedded in the IC, eliminating the need for a host MCU. This reduces board space and development workload.
The chipset complies with NFC Forum (WLC 2.0), enabling power transfer while maintaining compatibility with existing devices. It is positioned within the expanding NFC wireless power ecosystem.
The chipset is in mass production and has been adopted in SOXAI RING 2, launched on December 10, 2025, by SOXAI, Inc. SOXAI RING is a Japan-developed smart ring for sleep management that captures and analyzes sleep data. SOXAI RING 2 incorporates an optical vital sensor, temperature sensor, accelerometer, Bluetooth Low Energy communication, and NFC wireless charging. It features Deep Sensing, a proprietary photoplethysmography (PPG) sensor for improved measurement accuracy.
Evaluation boards and reference designs are available to support integration. Application examples include smart rings, smart bands, smart pens, wireless earphones, and other compact wearable devices.
