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BQ25180: Improper charging when battery connected prior to input voltage

Joseph Lee
Prodigy 10 points
Part Number: BQ25180
Other Parts Discussed in Thread: BQ27427,

Tool/software:

Hi, I am currently working on a design where I am using the BQ25180YBGR (in combination with the BQ27427 fuel gauge IC) and have observed a very strange and concerning failure mode with the initial prototype samples during bringup.

In particular, if I provide 5V power to the VUSB bus before connecting a battery to J4 then everything works as expected and I am able to adjust charging current via register settings etc. However, if battery is plugged in before VUSB then when 5V is provided to VUSB I measure a very high current draw (~1.5A) regardless of maximum input current limit register setting and measure a high voltage (4.6V) across the lithium battery for a few seconds before the lithium battery's internal protection cuts in and disconnects it from the circuit at which point I measure 5V across the battery terminals. I have attached a screenshot of the relevant part of my schematic. Can anyone provide any insight, debugging next step suggestions, or possible reasons for this issue?

Thanks!

  • 0
    TI__Genius 10190 points

    Hi Joseph,

    Thanks for reaching out.

    The maximum input current limit setting of the BQ25180 is 1.1A, so if you're seeing that the input is supplying 1.5A and also measuring 5V from BAT to GND, it sounds like the input could be shorted to the battery somewhere.

    The connection of the battery looks correct in your schematic: the battery connector goes to the BAT pin of the gauge, through the gauge's integrated sense resistor, and out of the SRX pin to the BAT pin of the charger.

    How many boards are you seeing this issue on? With the battery removed but VBUS connected, do you measure 5V on VIN? Is VUSB connected to anything else in your schematic? If you plug the battery in before VUSB, does charging occur normally?

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 10 points

    Hi Alec,

    Yes, I also thought that maybe the input was shorted to the battery but that wouldn't make sense for two reasons: 1) if I measure with a multimeter between those two pins I see an impedance in the MOhm range and 2) if I make sure to supply VUSB BEFORE connecting the battery then the device behaves perfectly normally.

    I ONLY see the high current draw and high output voltage if the battery is connected prior to VUSB being supplied.

    I see 4.2V exactly when VUSB is connected but battery removed. If I then attach a battery then the whole system runs completely as expected (normal input current, normal battery charge cycle, etc.)

    However, if I first plug in the battery, then connect VUSB, I get 1.5A or so of current draw. If I then quickly unplug the battery while leaving VUSB connected then I measure 5V on the battery pin.

    Currently I am only seeing this on one board as I have only finished bringing up the first prototype. I do have X-ray images from this board showing that soldering under the part appears normal (no bridges, excessive voids, etc.) which I have attached here as well.

  • 0 in reply to Joseph Lee
    TI__Genius 10190 points

    Hi Joseph,

    This behavior is abnormal and not the expected behavior of the device. The input current limit (ILIM) cannot be exceeded, regardless of whether the input source or the battery is connected first. It's possible the device may have been damaged or there is an unintended path from the input to the battery on your board.

    Does the issue still occur if the device is replaced with a new device? I understand you are still bringing up other boards. It would be very helpful to know whether this issue is happening on multiple boards or just this one.

    The most direct way to isolate the root cause of this issue would be to perform an A-B-A swap, which will determine whether the board or the IC is the problem. If other boards do not show this issue, I recommend the following:

    (A) Remove the suspect part (A) from the original failing board.

    (B) Replace the suspect part (A) with a known good part (B) and check if the original failing board now works correctly.

    (A) Place the suspect part (A) onto a known good board and see if the issue follows the part.

    Please let me know what you find.

    Best regards,

    Alec