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BQ4050: Soldering Battery Terminals to PCB Causes FUSE pin to Assert and Blow Fuse

Matthew Kordbegli0
Prodigy 120 points
Part Number: BQ4050
Other Parts Discussed in Thread: EV2400

I have the Fuse drive section of the BQ4050 configured as in the schematic below.  I verify that the FUSE signal is low.  Then, I attempt to solder the positive terminal of a battery to my PCB.  After the soldering process, the FUSE pin is asserted, turning FET Q7 on.  As a result, when the top most battery is soldered to the PCB the enabled FET causes a path to ground blowing the FUSE.  At the moment, I believe this to be the result of the solder tip being energized and causing a voltage differential on my PCB.  Have you ever encountered something like this before?  If so, how do I get around it?  Let me know if you require any additional information. 

Thank you,

  • 0
    Prodigy 120 points
    Update:

    The problem is independent of the soldering iron.
    If I have the EV2400 box disconnected from my board and I touch the +battery terminal wire to the contact pad; the Fuse signal will assert and remain in that state with power connected until I manually reset it. If I repeat the process with the EV2400 connected, the battery management studio will lose communication but the Fuse signal will remain low. The general problem at this point is, with the EV2400 NOT connected, how do I connect the battery terminals without activating the Fuse pin?

    Notes:

    I have tried applying voltage at the PACK+,PACK- terminals while attempting to complete these steps without success.

    When I say that the Fuse pin is asserted I mean that the voltage at the gate of my Q7 FET is ~2V (enough to turn the FET on). Not 7V as stated on page 13 of the BQ4050 datasheet
  • 0 in reply to Matthew Kordbegli0
    TI__Mastermind 25955 points
    Hi Matthew,

    When creating your golden image for programming in production, please leave the safety and protections disabled. After welding the cells, but prior to sealing the gauge, enable the safety and protections.

    The EV2400 may be disconnected for the welding step.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 120 points
    Good morning Bryan,

    I'm convinced that the problems were caused by a design oversight and I was able to resolve the issues by making some hardware adjustments to the PCB. Along our design path, we decided to remove the PTC thermistor, (P1 and P2 in schematic above), which left those pins floating. Based on page 40 of the BQ4050 datasheet, this is not ideal and a PTC fault is one of the permanent failure modes, which I believe would cause the hardware/software symptoms I was observing. I corrected the issue by grounding pins 23(PTC) and 24(PTCEN) at VSS and cutting the trace between pins 32(VBAT) and 24(PTCEN). After those adjustments, I have built several boards and performed moderate testing on each without issue. Thank you for your suggestions and please let me know if you would like to exchange any additional information

    Regards,
    Matt
  • 0 in reply to Matthew Kordbegli0
    TI__Mastermind 25955 points
    Hi Matt,

    I'm glad to hear that you have resolved the issue!

    Please let me know if any other issues arise.

    Sincerely,
    Bryan Kahler