Wireless power supply IC for smart rings

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 miniaturisation, is attracting increased attention, with adoption accelerating in next-generation wearables. Following the successful commercialisation of the 1W ML7660/ML7661, ROHM has developed the ML7670/ML7671 chipset optimised 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.

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.

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