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BQ40Z50-R2: After spot welding the battery positive VC1 and VC2, we found the SCL and SDA keeps low.

Statham Su
Genius 4990 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: EV2400

Hello Sir:

Please refer our schematic and gg file as attached files.

Our production processes shows below.

1. PCBA testing, calibration V/I/T and .srec download to BQ40z50-R2, which FW is 2.11.

2. Spot welding the battery point VG, VH and VP (refer schematic), and retest all PCBA functions (such as protection points and capacity learning)

Whatever at this pilot run, our failed rate is around 10%, make 300pcs prodcuts and has 30pcs failed products.

And all failed condition were SCL and SDA keeps low.

Whatever we use charging voltage or EV2400, it's no use.

Can you help to figure our what's wrong with our gg file or schematic or anything?

Please help to provide recommendations for us.

Looking forward your feedback.

Thanks a lot.

MDB-6732.pdf

  • 0
    TI__Guru** 105870 points

    Hello Statham,

    Were the batteries spot welded while attached to the gauge or separately? If the packs are spot welded with the gauge attached this could cause damage to the gauge.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi  Keller

    Good day!

    The sequence of spot welding is from low to high (VG to VP) and the spot welding is separated.

    Thanks a lot.

  • 0 in reply to Webber Lin
    TI__Guru** 105870 points

    Hello Webber,

    Do you see the communication lines held low by the gauge when you use the EV2400? The EV2400 has internal pull-ups, so it should be high until there is communication. What does your circuit use to pull up the communication lines?

    There should be no reason that before the spot welding the gauge passes V/I/T checks, then after spot welding with the gauge disconnected the gauge fails. The only thing between these points would be physical or ESD damage to cause some kind of failure.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi  Keller

    Good day!

    SMBC/SMBD pull high via EV2400.

    The pack can't be waked up after spot welding that we try to discharge the battery(without PCM) directly until 2V. Then charge the battery, the abnormal situation is resolved. 

    It seems not the ESD problem here.

    Thanks a lot.

  • 0 in reply to Webber Lin
    TI__Guru** 105870 points

    Hello Webber,

    Yes the EV2400 will pull the lines high, does the gauge when it is in this state pull the lines low?

    So the issue can be resolved by essentially power cycling the device? If the device is in shutdown mode you will need to apply voltage on the PACK pin in order for the gauge to wakeup and start communicating again after it losses power.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi  Keller

    The Gauge is pull the lines high.

    It can be solved by Power-on reset on the battery side.

    Because it takes a lot of production time to perform this action after spot welding.

    We want to know why we need Power on reset on the battery side.

    Thanks a lot.

  • 0 in reply to Webber Lin
    TI__Guru** 105870 points

    Hello Webber,

    It seems the issue is not the spot welding process, since you only disconnect the gauge from the batteries and reconnect them after spot welding. Do you see the same issue occurring by doing the same process (disconnecting and reconnecting the batteries)? By shorting PACK+ to BAT+ is the issue resolved? The only time the gauge should not talk over communication is in shutdown or there is no power (third is no communication from damage).

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi Keller

    Good day!!

    1. Do you see the same issue occurring by doing the same process (disconnecting and reconnecting the batteries)? 

    --- No, it didn't happen after power-on reset.

    2. By shorting PACK+ to BAT+ is the issue resolved? 

    --- We tried but it didn't solve the problem.

    3. The only time the gauge should not talk over communication is in shutdown or there is no power (third is no communication from damage).

    --- The Gauge is pull the lines high and we have charge the pack after spot welding.

         We have to power-on reset directly on the cell and charge the battery pack in the same time for resolving this problem. 

         But it wouldn't be the way for production.

    thanks a lot.

  • 0 in reply to Webber Lin
    TI__Guru** 105870 points

    Hello Webber,

    I do not understand how only the spot welding process would cause an issue if the only thing that is occurring is disconnecting and reconnecting the batteries. What is the cell connection process after the spot welding? Is the same order from lowest cell to highest cell voltage used for both test methods? Make sure it is always low to high cell connections.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi  Keller

    Good day!!

    We have found the root cause, thanks for your help.

  • 0 in reply to Webber Lin
    TI__Guru** 105870 points

    Hello Webber,

    Thanks for the update, what was the discovered root cause?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi  Keller

    Good day!!

    We designed a gap in the self-control protector.
    We need the solder the gap after completing Pre-Test.
    The abnormal condition is due to shorting on the TS1 test point during the soldering process.

    thanks for your help.