ROHM has launched a new wireless power supply chipset designed specifically for ultra-compact wearable devices such as smart rings and bands. The solution combines a receiver (ML7670) and transmitter (ML7671), leveraging NFC technology to enable efficient short-range charging.

For eeNews Europe readers working on wearable and low-power designs, the move highlights how NFC-based wireless charging is emerging as a practical alternative to Qi in space-constrained devices. It also reflects the growing demand for highly integrated solutions that reduce both footprint and design complexity.

NFC charging gains traction in wearables

The rapid growth of the smart ring market—particularly in healthcare and fitness—has exposed limitations in existing charging approaches. Wired charging is impractical for such small form factors, while Qi wireless charging faces challenges due to coil size constraints.

ROHM’s chipset addresses this by operating in the 13.56MHz NFC band, which allows much smaller antennas and supports proximity-based power transfer. This makes it well suited for compact designs where space is at a premium.

The ML7670/ML7671 builds on ROHM’s earlier 1W ML7660/ML7661 devices but is optimized for lower power applications, with a maximum power transfer of 250mW. The integration of key components, including switching MOSFETs, reduces the need for external parts, helping to shrink board size and improve efficiency.

High efficiency in a tiny footprint

A key differentiator is the receiver IC’s compact size—just 2.28 × 2.56 × 0.48mm—combined with a reported power transfer efficiency of up to 45% at 250mW. ROHM attributes the performance gains to optimizations in coil matching, rectifier design, and reduced switching losses.

Another notable feature is the integration of all required firmware for wireless power delivery directly into the IC. This removes the need for a host MCU, cutting both development effort and overall system footprint.

The chipset is compliant with NFC Forum WLC 2.0, ensuring compatibility with existing NFC ecosystems and enabling simultaneous data and power transfer scenarios.

ROHM says the devices are already in mass production and have been adopted in the SOXAI RING 2, a recently launched smart ring targeting sleep monitoring applications. Evaluation boards and reference designs are also available to support integration.

Looking ahead, the company plans to continue developing miniaturized, low-power solutions aimed at expanding the capabilities and convenience of next-generation wearable devices.