The AirFuel Alliance (AirFuel) has a broad technology platform encompassing resonant and uncoupled technologies. With resonant chargers, the 6.78MHz frequency of magnetic resonance can achieve a much larger vertical range of 50mm or more. Multiple devices can be charged using a single larger transmitter coil, which also provides a larger active charging area or “sweet spot”. AirFuel's resonant technology allows for a more flexible near-field charging experience and offers more positioning freedom over inductive solutions. This technology is suitable for devices that have high metallic content, have compound shapes (unlike a smartphone), or can benefit from multi-device charging.
But there are some challenges with resonant charging. The power has to be switched very fast. This means that the MOSFET’s gate characteristics have to fit in the 150ns cycle requirement. On the other hand, minimum parasitic capacitances have to be reached, while efficient voltage conditioning to control the output power is needed.
Infineon, through the partnership with Spark, is the only company that offers both inductive and resonant technologies, allowing a custom-tailored solution that uniquely meets all application’s requirements (figure 3a and 3b). Both inductive and resonant solutions can conform to a standard or be proprietary to the application, depending on the market needs.
Robust and reliable FOD
Standard Foreign Object Detection (FOD) methods rely on the large primary coil winding for detecting foreign objects, which reduces sensitivity and signal to noise ratio. Smaller objects are difficult to detect, due to the small impact on the magnetic field of the much larger primary coil. Existing transmitter solutions measure the parameters needed for the power loss calculation (voltage and current) at the DC supply of the inverter. This distorts the measurement when compared with the actual values at the coil, causing an inaccurate transmitter loss calculation.