Hello there,
We have design our own coil for the BQ51050 together with the BQ500212A transmitter. As first coil design we fabricated a 14uH inductance with Q=32. The coupling factor is poor with a value of 0.3.
The wireless charging works even for an output current of 1A using a battery emulator and a distance of 5mm. However, the ping voltage is too close to the limit: any misaligment or distance increase avoided the ping so we decided to fabricate a coil with higher inductance.
In this second case, we fabricated a L's=53uH (Ls=51uH) inductance again with Q=32 and K=0.3 and modified series and paralell capacitor accordingly (Cs=47pF and Cp=400pF). What we found here is:
1. We had to increase Cp because the transmitter did not recognize the receiver for 5mm so we had to further reduce the distance.
2. The output current (keeping RLIM to 300 Ohms) did not reach to 1A but 800mA although the transmitter frequency was at 125KHz.
Do you have any tip of what is happening? Maybe is a question of the parasitic resistance of the coil and low coupling?
Best regards,
Hector.