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BQ76952: BQ76952 IC fails when power to host controller is removed

Praveen Reddy
Prodigy 10 points
Part Number: BQ76952

I am using BQ76952 in one of our projects,  host controller is interfaced to BQ76952 on I2C.  Host controller has a separate power supply (5V_ISO & 3V3_ISO) 

The power to host controller is switched off when board is not in use.

Board was working fine for last one month, suddenly one board failed. following are the observations

  1. No I2C communication
  2. BQ76952 getting heated up
  3. Voltage on REG18 is 0.6V

After replacing BQ76952, board works fine for few hours after which it fails. (tried 4 times)

Please refer attached schematic.

kindly request to provide any information on the issue.

  • 0
    TI__Mastermind 42060 points

    Hello Praveen,

    It sounds to me that something is damaging the device. Now, we would want to understand why. Do you see any shorted pins? Or any unintended currents?

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    No shorted pins, facing issue in multiple boards.

    Current in VBAT pin is around 1.4mA ( working IC), for damaged IC it is 7mA.

    We are using 2V cells, voltage at VBAT is around 32V.

    always damage is observed when board goes through a power cycle ( cell connections are active during power cycle).

    Regards

    Praveen

  • 0 in reply to Praveen Reddy
    TI__Mastermind 42060 points

    Hello Praveen,

    What goes on during a power cycle? What is the procedure there? Do you have any logs? 

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Praveen Reddy
    TI__Mastermind 25650 points

    Hi Praveen,

    How is the device being power cycled? Through RST_SHUT or by a command? If it is via RST_SHUT, could you share the portion of the schematic that shows the circuitry that controls the pin?

    Regards,

    Max Verboncoeur

  • 0 in reply to Luis H. S.
    Prodigy 10 points

    Hello Luis,

    In further testing we have done the following

    1) Removed all the host components on board. Only BQ76952 is active.
    2) Removed additional 5V & 3V3 power supply components from board
    3) Powered BQ76952 only through cell voltages.
    4) IC was still damaging when the load on battery bank was switching.

    After further analysis found the cause for IC damage.

    1)There are multiple modules in the system, which are driven by a DC/DC power supply
    2)DC/DC module is connected to battery bank(60 cells) for input power.
    3)During power-ON condition, DC/DC module is inducing a negative voltage on lower battery cells.
    4)Lower cells in the bank showing high negative voltage (-50V w.r.t VC0) for short duration(150uSec) (screenshot attached).
    5)VC0-VC16 pins of BQ76952 are getting negative voltage for short duration and instantly damaging the IC.
    6)On first time damage, heat on IC is mild, upon repeated power recycle of DC/DC module, IC heat is increasing rapidly.

    We are working on further analysis and mitigation.

    Regards
    Praveen

  • 0 in reply to Praveen Reddy
    TI__Mastermind 42060 points

    Hello Praveen,

    Are multiple cells going negative? Which pins are going negative? Is the ground reference separate from the IC?

    I've never seen such a negative voltage before. The IC ground may be changing a lot to respect to the cell inputs. Most of the time we've seen a negative voltage is due to a fault protection when there's parasitic inductance/resistance between Vss and the VC0 input.

    Typically this only affects VC0 too, which in that case we recommend a Schottky diode and Zener to protect the VC0 pin. 

    Do let us know the results of your analysis.

    Best Regards,

    Luis Hernandez Salomon