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BQ51013B: wireless charging issue

Vijay Peddinti
Prodigy 20 points
Part Number: BQ51013B

Dear TI support team,

Greetings! 

I am sending this email regarding an issue with wireless charging. The voltage on the RECT pin is less than 1 V 

I am using the following:

1. TI BQ51013B

2. Wurth Electronics Rx coil 760308103206

3. Samsung wirelss charging pad (EP-PG920IWUGUS)

For computing AC1, AC2 capacitor values, I used the specified Ls value (=7.5uH), and for now I am using Ls' = 1.5 Ls. I contacted Wurth Electronics and should have a precise value soon.

Attached is the BQ51013B circuit, showing all the components. I reworked and connected the TS/CTRL to ground. The voltage ratings for the capacitors meets the specified values. 

Please let me know if you need any additional information. Also attached is the voltage waveform of the RECT pin, which is quite low. I have been trying to debug without much progress. I was wondering if you have any suggestions, any feedback is greatly appreciated. 

Thank you very much for your time, have a good day. 
Vijay

  • 0
    TI__Guru* 75876 points
    Check the TS / CTRL pin, it should not be open needs a 10k resistor to ground. This would trigger a shutdown.

    Take a closer look at the larger pulses (above 4V) see if you can see communication packets.
    Coil 760308103206 -- Small coils 28mm X 15mm are difficult they will have poor coupling and low gain, this can be off set by increasing the L value--But this coil has a low L value 7.5uH, 20uH or better would be recommended.

    The Low peak every 500ms may be a low power ping just to see if an RX is there.
  • 0 in reply to Bill Johns
    Prodigy 20 points

    Hi Bill Johns,

    Thank you for the feedback. The board is working.

    It was the TS/CTRL pin, I did try to rework and pull the signal to ground earlier. Perhaps the wire was not quite making contact to the pin. The space between the chip outline and the pad is very small and the pins are not exposed as it is a QFN package. I should have made the PCB footprint pins longer, it would have been helpful while soldering.

    I will make the necessary changes in the next version.

    Thanks again for your help, have a good day!

    Vijay