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Yaita-san,
1) The standard shows that the distance between the RX coil and the TX surface is 2mm +0.5mm / -0.25mm. The actual results of an individual system must meet these, but may work a greater distances.
2) and 3) We have done these types of evaluations internally with our EVMs as part of the Qi certification process. However, they are meaningless to any system other than the EVM. Any changes in the coil, shield, enclosure, and so on, would change the results. Having a final system that has metal near the coil impacts the results. Changing placement of the metal impacts the results.
Regards,
Dick
Yaita-san,
Your drawing is correct.
I have some current data, but it is not on the bq500212A EVM. The results would be similar. I can email you that data if you would like.
The key points to note are that each solution in its final form (receiver or transmitter) will impact the results.
For the Qi certification of a receiver, testing is done at the center of the TX and 5mm from the center in 4 directions. This allows the system to determine how the RX system would work in a normal environment. As such, a good design has similar results at all 5 points.
For the Z-distance, that depends on the plastics on the RX. Concern there it to minimize the thickness, have the proper shielding and maintain enough Z-distance for the rest of the circuitry in the system.
Regards,
Dick