A large number of low-power wearable devices such as smart watches, fitness wrist bands and headphones have been introduced to the market. This new family of electronic products is expected to grow and expand rapidly over the next few years. These devices are typically small and thin, with varying form factors and industrial design. Battery sizes might range from 100- to 300-mAh capacity, which determines the required charge rates.

The plug-and-jack style or micro-USB types of connectors have been the traditional way to charge such devices. But even these relatively small connectors are now too large for some of the new ultra-thin wearable applications. Connector contamination is an even greater problem due to the outdoor wearable environment.

Wireless charging is a solution to these problems and offers additional opportunities to designers. Existing semiconductor devices used for the Qi standard established by the Wireless Power Consortium (WPC) can be easily adapted for this lower-power application. The technology uses two planar coils to transfer power though a sealed case. For low-power wearable devices, a small, thin low-power receiver coil easily could fit into the back of the case or wristband area. Qi-compliant devices are a mature solution that can shorten development time, and the products are supported by the existing WPC infrastructure.

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