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bq51003 adjusts the Ccomm1 and Cc0mm2 ?

Jerry Chu
Genius 4915 points
Other Parts Discussed in Thread: BQ51003, BQ500215

Hi Expert,

My customer used bq51003, but the TX is not TI. When it pairs the power will drop, so the TX vendor adjusts the Ccomm1=22nF and the Comm2=2.2nF. They re-work 5pcs, after change the Commx, it can work. So, my customer ask us to confirm the solution is workable.

I have checked the WPC document, it mention about "The communications modulator consists of two equal capacitances 22nF in series with two
switches. The resistance value 10kΩ.". 

I think the communication waveform would be change and unbalance. Can we guarantee Ccomm1=22nF and the Comm2=2.2nF? Thanks!

  • 0
    TI__Genius 14890 points

    Jerry,

    Thanks for checking on this.  I have a series of questions that will be helpful for the final recommendation. 

    Is Qi-certification required for the bq51003 module?  If yes, I would recommend keeping both COMM capacitors the same.  The 22nF is not required, but as you note, keeping them the same will keep the communication waveform balanced.  the 22nF is the test configuration.

    Will the bq51003 module only be paired with your customer's TX?  If it will only run on the RX, then the right answer may be it's okay to do the mismatch.

    You can change the COMM values to determine the best fit.  Note that increasing the COMM capacitor values will (slightly) decrease your efficiency.

    My concern is that changing the capacitor values to create a working solution is masking the real issue.  

    Have you tested with transmitters other than the one from the customer?  I would strongly recommend that.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Genius 4915 points

    Hi Dick,

    They don't need to pass the QI-cetification and the bq51003 module only be paired with my customer's TX.

    Original design, bq51003 is paired with "I" company TX and it works well. But when they changed the TX solution, it can't work. We will ask the new TX module and test more TI RX. Thanks for the great information.

  • 0 in reply to Jerry Chu
    Genius 4915 points

    Hi Dick,

    I am changing the bq51013AEVM C13 to 2.2nF and get the below waveform. You can see the 2.2nF waveform's yellow mark, is it 2.2nF's side effect?

    I have tested bq51013AEVM with C13=2.2nF pairing with bq500215, it works well. 

    If my customer want to use 2.2nF for Ccm2 to mass production. Anything they need to do? Thanks!

    PS, CH1=COMM1=C8, CH2=COMM2=C13

    C13=22nF

    C13=2.2nF

  • 0 in reply to Jerry Chu
    TI__Genius 14890 points

    Jerry,

    I'm not sure I fully understand your question.  The COMM capacitors will influence how large the deviation is on the communication pulses.  We recommend using the same capacitors on COMM1 and COMM2 for a more robust solution.

    Testing with different sized COMM capacitors with the transmitters that will be used is a reasonable test.

    Regards,

    Dick