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BQ51003: C1 and C2 fine adjustment

Carlos Resende
Prodigy 125 points
Part Number: BQ51003

Hello,

I'm building a Qi receiver based on the BQ51003 and the WR301025-19M8-G coil from TDK. I've calculated the C1 and C2 according to the instructions specified on the BQ51003 datasheet, which resulted in the following theoretical capacitors:

C1 = 0.833962uF and C2 = 0.009426uF

Practically, I'm using the following capacitor values C1 = 0.47u+0.22u+0.1u+0.047u = 0.837uF and C2 = 8200p+1200p+18p=9418pF.

When I test my receiver with the AVID Qi FOD Transmitter v1.1 I repeatedly get the Device Detected message in the serial port (signal strenght between 55 and 59), and only if I very finely position the receiver on the transmitter the system passes from the Device Detected message into the FOD power transmission messages.

I'm assuming that this behaviour is related with a problem in the communication between the receiver and transmitter, which could be optimized by fine tuning C1 and C2. My question is: how can I do that fine tuning?

Thanks,

Carlos

  • 0
    TI__Guru* 75876 points
    Hi Carlos
    Double check the coil Ls' measurement. This is used for C1 calculation and is a measurement at 100kHz with coil in case and above the coil. The WR301025-19M8-G has an Ls value of about 13uH and the Ls' value will be different. But change suggested by your C1 value is quite large. Using 13uH I am calculating 0.195uF, for 0.834uF the Ls' would be around 3.3uH which looks very low.