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BQ500212A and BQ51051B : charge current is about half the expected current

C.A.
Intellectual 375 points
Other Parts Discussed in Thread: BQ51051B, BQ500212A, BQ51050BEVM-764, BQ51050B, BQ34Z100-G1

Dear all,


I am testing my wireless charger with BQ500212A and BQ51051B. The battery can be charged but its charge current is not what I expect.


If I understand correctly, the charge current is set by the sum of resistors R1 and Rfod (that are called Rlim). Then, Icharge = 314 A*ohm / Rlim. The Rfod is 200 ohm and I tried to have R1 = 470 ohm and 330 ohm that gives for Rlim 670 and 530 ohm. So I expected the following current :


- with 670 ohm : 314/670 = 469 mA and I got only about 220mA

- with 530 ohm : 314/530 = 592 mA and I got only about 265mA


I saw that JEITA specicification gives only half the current if the temperature is too cold or hot which could have been the answer to my question... but I measured the TS/CTRL pin and I got about 800mV during the 24 ms of TS measurement which is 0.8/2.2 = 36% of Vtsb. This value is between 19.6% and 47.8% and if I understand correctly, it means the temperature is normal...

Since I do not find any information about the Ros resistor (between RECT and FOD), I put 1 kOhm.

What value should I put for this resistor?

Anyone has an idea about my current charge issue?

Thank you in advance,

Best,

Christian

  • 0
    TI__Genius 14890 points
    Christian,

    The bq51050BEVM-764 is a good reference design. The EVM shows 42.2k for Ros. This sets the offset portion of the Foreign Object Detection calibration. RFOD sets the slope. Calibration can be done following the User Manual of the Foreign Object Detection (FOD) Calibration/Tuning Tool GUI found under the Tools & software tab of the bq51050B web folder. It is possible that the 1k Ros is having an impact.

    Try leaving the Ros resistor open to see how it impacts the charge current.

    Regards,

    Dick
  • 0 in reply to Dick Stacey
    Intellectual 375 points

    Dear Dick,

    Thank you for your message.

    Yes, I tried some other values for Ros some days ago and I managed to get a higher charge current. Sorry, I forgot to said this on this post.

    I tried to use the FOD Calibration tool but when I click on OK at the beginning, I get the following error message: "unknown protocol: c". So I cannot use this tool, anyone has experienced the same issue?

    I do not think I will be able to do a really nice calibration as is suggested in the document "Foreign Object Detection GUI User’s Manual" (SLUA731) because I need to get a source-meter such as the KEITHLEY 2425 and this device costs more than 10'000 CHF! As well, the AVID calibration tool costs about 3000 USD! That is too expensive for this development! We do not need any WPC/Qi certification.

    Thank you again Dick, I am trying to do a good calibration with the fuel gauge bq34z100-G1 now.

    Best,

    Christian

  • 0 in reply to C.A.
    TI__Genius 14890 points

    Christian,

    Are you able to get the full expected charge current?

    Another option for setting the current for FOD testing is a decade resistance box. If you choose this route, make sure to get one with a high enough power level.  Power resistors are also an option.  Using the transmitter planned for your system will not be as accurate as the AVID tool, but would give a first order approximation.  Look at the bq500212AEVM and the "bq500212A Wireless Power Transmitter I2C Interface" application note.

    I have not seen nor heard of the error message you're seeing. I will work with the GUI development team to see if we can reproduce the error.

    Regards,

    Dick 

  • 0 in reply to Dick Stacey
    TI__Genius 14890 points
    Christian,

    Can you send a screenshot of the error message?

    Thanks,

    Dick
  • 0 in reply to Dick Stacey
    Intellectual 375 points

    Dear Dick,

    Thank you for your messages.

    With 43 kohms for Ros (which is very close to the EVM value), I get a good behavior. I will try optimize this with the documents you quoted. Here are 2 screenshots showing the error.

    Best,

    Christian

  • 0 in reply to C.A.
    TI__Genius 14890 points
    Christian,

    Glad you have the system working as needed with the new Ros value.

    Thank you for the screen shots. What is your operating system?

    Regards,

    Dick