Part Number: BQ51013B
Other Parts Discussed in Thread: TIDA-00688, BQ25100, BQ51013
Hi, I have designed a development board hosting the BQ510313B wireless IC and the BQ25100 battery charger based on the SLUUB51, SLUU911 and TIDA-00688
For the lab tests I am using this coil from TDK:
I have calculated the series and parallel resonant capacitors based on the Ls and Ls’ (see 9.2.1.2.2 Series and Parallel Resonant Capacitor Selection of 51013b datasheet). I wasn’t able to calculate the exact Ls’ value and I used an approximation.
Please find attached the schematic design and the spreadsheet with the calculations
When I place the Rx coil above the Tx coil initially seems that everything is fine. I can measure 5V on OUT pin, the green led (connected between the output and the CHG pin) on the board turns ON, I measure around 8.5V on RECT pin (is that normal?) and also when I connect a battery on BQ25100 it charges with 16mA (that is exactly what I have calculated). Also the Tx pad I am using has a blue led build-in, lighting when there is Wireless Power Transfer (WPT).
However, after 4s the WPT stops and restarts after another 4s. So there is a 4s pattern between ON and OFF. 4s ON –> 4s OFF –> 4s ON –> 4s OFF etc etc
This is somehow related to the distance between the Rx and Tx coils and maybe the resonant capacitors network. I have noticed that when I increase the distance between Rx and Tx coils then this problem stops. When I bring back the coils to the initial position (closer to each other) then the problem returns. Also, I can confirm that this problem is irrelevant with the current drawn (16mA battery charging in my case). The problem persists with and without a connected battery. I have tested two Tx models so far and I am facing the same issue. The strange thing is that I found another Tx charger laying around and with this particular charger I have no problems... I am really puzzled..
Any suggestions?
