Qi-certified medium power transmitter reference design

24th May 2017
Lanna Cooper


Apple touts its new Airpods as wireless, effortless, and magical, a description that aptly fits another emerging technology: wireless charging. Wireless charging sends a flow of electrons to a device’s battery using either ultrasound, solar, or electromagnetic energy, in place of a tethered AC charger.

Wireless power transmission technology is not just indistinguishable from magic: it’s become as invisible as breath and air; a flow of energy more akin to the ancient Chinese principles of material energy, or life force, termed Qi - which aptly enough, is the name of the most popular emerging wireless charging standard.

The Qi (pronounced 'Chee') wireless charging standard is backed by an association of 200-plus companies, including phone and tablet makers, semiconductor suppliers, and wireless service providers.

The standard is based on electromagnetic induction between planar coils and consists of two types of devices - a base station connected to a power source that provides inductive power to the mobile device. The base station contains a power transmitting coil that generates an oscillating magnetic field; the mobile device contains a power receiver receiving coil. The magnetic field induces an alternating current in the receiving coil using Faraday’s law of induction.

To enable designers to equip mobile devices with Qi wireless charging, Rohm Semiconductor has developed a Qi-Certified Medium Power Transmitter Reference Design using its BD57020MWV wireless power transmitter IC. The WPC Qi standard was developed to meet the need for fast wireless charging in the portable mobile market, and it expands the power range from 5W (low power) to 15W (medium power).

ROHM is the first supplier in the world to offer a reference design for medium power that has passed interoperability tests with more than 200 Qi-certified devices and has successfully acquired Qi certification under the medium power specification.

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