After the great help I received from Bill and Dick I now have a working Tx design. However I noticed the the Tx/Rx system has good spatial freedom in the Z direction once communication is established, but requires a very small Z gap to establish communications. This may not be important to my end use, but I am curious and this may help others.
While I do not have specific measurements of the gaps yet I will provide an example. The Qi retail Rx I have is for a cellphone. Without a case on the cell phone the Rx communicates and charges the cellphone easily. With a case, communication cannot be established. However if I establish communication and then add a space equivalent to the thickness of the cellphone case, charging operation proceeds as expected.
So how can I improve the Z spatial freedom? I know resonance frequency is out of the question to maintain compliance with the WPC/Qi standard. Tx coil geometries seem to be established and they appear to be very similar in design to one another. I suppose you could raise the coil switching voltage, but that would complicate and defeat the purpose of a bq500212a design.
Since you are far more experienced than I am in this area, do you have any coil or other suggestions? I am unsure, but would a new Tx coil design violate compliance with Qi? I am currently using the Wurth Electronic 760-308-101 24uH coil instead of the EVM's Wurth Electronic 760-308-111 6.3uH so my performance may vary from the EVM.
Thanks for your time.
