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BQ25886: My battery is not charging

Gerald
Genius 9570 points
Part Number: BQ25886

Hi Team,

May I ask for your help and expertise? My customer concern is shown below:
"I have a question regarding BQ25586 IC which we are using for charging the Batteries (2 cell series Li-ion). I gave USB supply via Laptop to the board and also I tried with Bench power supply 5V (by shorting to VBUS pin). We used all the RLC values as specified in the datasheet. I did few changes as changing R values at STAT and /PG as 200ohms instead of 10k and my Vref is 3.3V. So, My output at Vsys is good I am able to see 5V. However, my Vregn is low and D1 and D2 LEDs are not glowing and my battery is not charging. Pls help me with this

Why there is no voltage at Vregn (pin 11) and then we are connecting same pin to TS (pin 7). In data sheet it's written as when TS is out of range (what are the values of range) then charge is disabled. Is that the reason ?

For schematic please let me know if you need it and I will send it thru email. 

I hope you can help us with this. Thank you.

Kind regards,
Gerald


  • 0
    TI__Guru** 105760 points

    Hello Gerald,

    Please share the schematic and layout if possible.

    One note is to make sure the absolute maximums aren't exceeded for PG and STAT pins, which is 6mA. I'm not sure the diode they are using and if the current is being exceeded.

    The conditions for REGN to turn on are defined in the datasheet: 8.3.3.3 Power Up REGN Regulator (LDO)

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Hello Gerald and Wyatt,

    Sorry for the late reply. Hope you both are doing great and I hope you have the schematic. So, to make it very clear I want to explain it again. I am using Bench power supply (also tried laptop 5V) via USB to give power to BQ25886 and I have seen No output (0V) and then I connected 2 series Li Batteries (Now my board is battery powered). So, at input of the chip, I am applying 5V from the bench supply and 7.2V (3.6+3.6V) from the battery which makes the /PG LED turn ON but the STAT LED keeps blinking (as stated in Datasheet 1Hz when fault happens) but my Vsys is 5V which is good but no Volts at Vregn. On second note I thought, ok may be the batteries are fully charged that is why it is not charging anymore (as stated in  8.3.7.3 Charging Termination data sheet) and I replace two other batteries which are very low (total=3.6V) at that time no Vsys and Not charging at all. 
    Thanks
  • 0 in reply to Wyatt Keller
    TI__Genius 9570 points

    Hi Wyatt,

    Please be informed that I sent the schematic to your email.

    I hope you can further help us with this.

    Thank you so much.

    Gerald

  • 0 in reply to Gerald
    TI__Guru** 105760 points

    Hello Wende,

    The schematic of the charger looks okay to me. Make sure the cable lengths are short for testing to eliminate and inductance issues. Also is there a load on SYS during the tests?

    I would also double check all the connections to make sure they are secure and there's no shorts. Is this occurring on all test boards or only one?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Hi Wyatt,

    Thank you for the reply. The battery cable length is 13cm. Bench supply cable length is 90cm. 

    We didn't connect the device load on Vsys, just for one DC/DC converter input, the load should be very light (~mAs).

    Yes, occurring on all boards.

    Thanks

  • 0 in reply to wende li
    TI__Guru** 105760 points

    Hello Wende,

    Can you share the layout as well? Have you tested the system on an EVM previously?

    Sometimes if there's a large capacitance on SYS the charger will hit OCP before starting up properly.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Eval_Base_Board.zip

    Hi Wyatt,

    The gerber file was attached. We didnit test EVM previously yet. 

    By the way, what is the maximum capacitance on SYS?

    Thanks

  • 0 in reply to wende li
    TI__Guru** 105760 points

    Hello Wende,

    You can reference the checklist for specific components, your SYS capacitances are near the recommended values: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/849874/bq25883-bq25883-schematic-review

    I didn't see anything that stuck out to me in the schematic or layout, it is a little hard to tell all the signal/power paths from the .art files. The only thing is try to shorten the traces to the switching inductor.

    Can you capture some waveforms of the VBUS plugin of VBUS, IBUS and SW node?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points
    Hello Wyatt,
    Thanks a lot for your reply. Because find the attachment for waveforms as you requested. For Vbus, I used Bench power supply 5V and Yellow colour DC 5V waveform is VBUS and for SW pin, again 5V across 17 and 18 pins of BQ25886 chip. As you can see in the above pic, Only /PG is glowing (HIGH) while the STAT pin is still flashing at 1Hz (which states fault). Vbus=5V, SW=5V and my Battery is 7.37V
    And as you mentioned about shorting the Inductor, I bypassed a small wire across L1 (as per schematic), I could not see charging but STAT LED is off (LOW). As per the data sheet, it means either charge disabled or Fully charged (I do not think it is fully charged because I do not see any current value in Bench power supply or should I discharge battery a bit until Vbus>Vbat and test it). 
    And how can I take waveform for Ibus. Sorry, could not be able to do it and also do you recommend us to buy an Evaluation board and try it once. Looking forward for your reply  
  • 0 in reply to wende li
    TI__Guru** 105760 points

    Hello Wende,

    I will take a closer look tomorrow, but I would recommend getting an EVM to test with as well, it always helps to have a good reference to work with.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Guru** 105760 points

    Hello Wende,

    I meant to reduce the trace length of your PCB layout for the inductor paths, not to short the inductor. Shorting the inductor may cause damage if any of the voltages or currents exceed the absolute maximum ratings.

    I would also recommend adding more capacitance to your PMID pin to prevent inrush current issues. Is the blue waveform the SW? Can you also show a waveform during the initial VBUS plugin of a longer timeframe on the scope?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 50 points

    Hi Wyatt,

    We will buy EVM, and feed back to you after test.

    Best regards

    Wende

  • 0 in reply to wende li
    Prodigy 30 points

    Hello Wyatt,

    Sorry for late reply. It took time to get the EVM delivery. I have a quick question about EVM Board. If I give 5V at VBUS (via bench power supply), Can I directly connect Battery to BAT & PGND pins (replacing Battery Simulator- we do not have any) ? And I followed all the Jumper Connections as mentioned.

    Thanks. 

  • 0 in reply to GOPINADH TALLURI
    TI__Guru** 105760 points

    Hello Gopinadh,

    Yes you can directly connect a battery to the BAT and PGND terminal of he EVM. A battery simulator is not required to use the EVM.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hi Wyatt,

    Thanks a lot for quick response. Yes, Both LEDs are ON, and my Battery(2S) charging. EVM Board is working very good. I see a Voltage at REGN, SYS, PMID pins. I am really not sure why our application board is not working. I will try to compare EVM to my schematic and update you soon. Thanks a lot for your patience every time we ask questions.  (VBUS: bench power supply 5V and :0.16A) 

    Regards

    Gopinadh 

  • 0 in reply to GOPINADH TALLURI
    TI__Guru** 105760 points

    Hello,

    I will take a closer look at your layout and schematic as well, I would double check to make sure all the connections on your board are okay and there's no bad connections. If all the connections are good then there must be something with the layout/schematic.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 30 points

    Hello Wyatt, 

    Do you suggest us to re-layout the whole board again as per the specs in data sheet and EVM ?

    Thanks

  • 0 in reply to GOPINADH TALLURI
    TI__Guru** 105760 points

    Hello,

    I would try to follow the recommendations on the schematic checklist along with using the EVM as a guide. The capacitor ratings on the checklist are after they have been de-rated.

    I didn't review the whole system schematic, just the charger section, so I'm not sure if something else may be causing the charger to behave this way.

    Sincerely,

    Wyatt Keller