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[FAQ] BQ76930: or bq76940: Zero volts reported after boot

WM5295
Guru 54715 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ76940,

Why do some cell voltages read 0 after boot with the bq76930 or bq76940?

  • 0
    TI__Guru 54715 points
    The bq76930 and bq76940 have cells organized in groups of 5, each with its own power pin.

    If an upper group is not powered, it will cause an error in the lower group and that group will not report cell voltages. For a bq76930 an error in the upper group will cause all cells to show 0V. For a bq76940 an error in the top group will show 0V for cells 6 through 15 while cells 1 through 5 will show voltages. An error on the bq76940 middle group will cause all cell voltages to be 0V.

    Common things to check:

    Be sure the cells are connected.

    Be sure filter components and IC pins are properly soldered on the board.

    Be sure the CAP2 and CAP3 capacitors are in place and not shorted.

    Be sure the TS2 and TS3 thermistors are attached or pull down resistors are in place. The TSn pins are inputs and must have a pull down resistor or thermistor to the proper reference voltage for the part to operate: TS3 to VC10X, TS2 to VC5X, TS1 to VSS. When thermistors are mounted remotely and connected in system with a connector, be sure to provide a substitute resistances to simulate the thermistors during board test.