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BQ76940: BQ76940 ADC issue

Skate Lu
Intellectual 870 points
Part Number: BQ76940

I designed a 13S E-Bike battery pack with BQ76940. I know that bq76940 has three ADC. I now have a battery that was returned from the end customer and I found that two ADC were damaged.The following is our schematic diagram and the picture of the communication.

What circuit can prevent ADC damage?Because my product will be mass produced, if this problem is not solved, my project may be terminated, thank you!

  • 0
    TI__Guru 54715 points

    Hi Skate,

    The System_Status register shows the DEVCE_XREADY set, so there is a communication problem between the cell groups.  Since voltages display for the bottom group the middle group is probably functioning but can't send data due to the fault.  The top group is likely the problem.  Some good things to check:

    • Check the voltage across the CAP2 capacitor C87, it is likely 3.3V from the registers, 
    • Be sure the CAP3 capacitor C81 and the pin are not shorted.  The cap should have 3.3V if operating.  Likely it is 0 or low voltage.  If 3.3V and the registers won't display the part is likely damaged.
    • Be sure the TS3 pin is still connected to the thermistor.  If the thermistor opens C85 can hold a voltage on TS3 and the top group won't start.
    • Be sure the TS3 signal has not developed a resistance to a lower voltage, TS2 or VC5X.  If pulled below VC10X the top group won't start.
    • Be sure the connection to C14 is not broken, the top group must have power to BAT pin.
    • Check that BAT pin voltage is approximately C14.

    Also look for signs that TS3 or CAP3 may have contacted a high voltage.  Overvoltage on these pins may damage the top group.

  • 0 in reply to WM5295
    Intellectual 870 points

    Thanks for help！

    I'll follow your advice and recheck my circuit.