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BQ51051B: Charging phase does not start(end correctly after having decreased I bulk

Gianluca Milani
Prodigy 190 points
Part Number: BQ51051B

Hello,

I am using this chip on my board to recharge a Li-ion battery. As long as I set as parameters Ibulk = 500mA and Iterm = 50mA, during the recharge phase both the starting and the termination phases were correctly performed. Then, I had to decrease the Ibulk due to battery constraints. Since the minimum value allowed from the datasheet was 500mA, I asked to TI Support.

They told me that it was possible to go down to a value of 100mA for Ibulk and 30mA for Iterm (see the figure attached). So, I set the Ibulk=190mA and the Iterm to 30mA.

But then, the following issues appeared:

1) when the battery is low and I try to recharge it with the device turned on, the recharge does not start until I turn off the device. A possible explanation of this behavior is that the current requested at the power on from my application is greater than 190mA, could you confirm this?

2) Ending phase: the LED which turns on only when the chip is in the recharge phase (see the image attached) does not turn off anymore if I leave the board under recharge, while before the modifications it turned off after the expected recharge time.

Do you have any suggestions on this?

Thank you,

Best regards,

Gianluca Milani

  • 0
    TI__Guru* 75786 points

    Hello

    I am checking on your question and will try to get back to you today.

    Couple of things that will help:

    1.) Which transmitter are you using?

    --The Qi standard defines a lot of system behavior but restart after Charge Complete if flexible and I have seen some that will require 15min to restart.

    2.) Do you have a scope capture of the RECT voltage when unit does not restart?

    ---This after charge complete the released and unit is trying to restart.  The RX should stop sending EPT01 as first pulse when power is applied.

  • 0 in reply to Bill Johns
    Prodigy 190 points

    Hello, 

    thank you very much for your answer.

    - I am using some commercial transmitters (see the image attached). What do you mean that they require 15 minutes for restart? The problem in my case (my second bullet point) is that the recharge seems to never complete, because the led is always turned on.

    - I cannot access the office until next week because of pandemic, as soon as I can I will return to you with the scope measurements. Why do you say "after charge complete?". Sorry if I did not get, by the way the problem in this case (first bullet point) is when the battery is low (no power anymore inside) and I try to recharge it while the device is 'ON'.

    Thank you again,

    best regards

    Gianluca

  • 0 in reply to Gianluca Milani
    TI__Guru* 75786 points

    Hi Gianluca

    1) when the battery is low and I try to recharge it with the device turned on, the recharge does not start until I turn off the device. A possible explanation of this behavior is that the current requested at the power on from my application is greater than 190mA, could you confirm this?  -- Bill J - The current will be limited to 190mA and will divided the current between load and battery, it will take longer to charge the battery.  Note that unit has a 10hr timer that will set the fault if charge is not completed.  Charge not starting could have several causes, the RECT pin is a good indication of what they system is doing, is it not reaching target voltage, is it having communication problems or other.  Also noise from the load will get passed thru to TX and can possibly interfere with communications, is the load active and generating low freq load change in the 2kHz to 4kHz range?

    I did set up a unit in the configuration and was able to start consistently down to 3.0V and terminate. Did see unit send EPT01 (Charge Complete).

    More to follow.

  • 0 in reply to Bill Johns
    TI__Guru* 75786 points

    Hi Gianluca

    2) Ending phase: the LED which turns on only when the chip is in the recharge phase (see the image attached) does not turn off anymore if I leave the board under recharge, while before the modifications it turned off after the expected recharge time.  -- Bill J - At Ending Phase (charge complete) the RX will send EPT01 packet (End Power Transfer Charge Complete) and the TX will turn off.  At this point the LED will go out, RECT voltage to 0V. The charge current will go to 0mA, can check voltage at ILIM pin.  Current out of pin is proportional to output current, ratio is 1 to 360 and should be 0.

    The TX will need to power up the RX and check if it needs more power, this power up is often a short ping at 5 sec rate.

  • 0 in reply to Bill Johns
    Prodigy 190 points

    Dear Bill,

    thank you very much for your answers, they have been very useful.

    As soon as I will go in the lab I will perform some tests and measurements and I'll let you know if I solved the issue.

    Thank you , best regards

    Gianluca

  • 0 in reply to Gianluca Milani
    Prodigy 190 points

    P.S.: Do you think that if I increased the termination current from 30mA back to 50 mA, this would be a possible easy test/solution for the never ending phase?

  • 0 in reply to Gianluca Milani
    TI__Guru* 75786 points

    Hi Gianluca

    Increasing termination to 50mA may help.  At this point not exactly sure what is causing the problem.  But termination at a higher current corresponds to higher operating point and possibly better communication.