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BQ76907-Q1: During the cell balancing process of BQ76907, are the MOSFETs on the DSG and CSG turned on or off?

Alon Chen
Intellectual 425 points
Part Number: BQ76907-Q1
Other Parts Discussed in Thread: BQ76907

Tool/software:

Hi Team，

During the cell balancing process of BQ76907, are the MOSFETs on the DSG and CSG turned on or off? I can't find any relevant description in the specification. Please help me take a look. Thank you.

  • 0
    TI__Intellectual 880 points

    Cell balancing does not directly disable the DSG/CHG FETs, thus if they are on when cell balancing occurs they will remain on.

    However, if cell balancing triggers some fault (such as an over temperature fault) then this fault could disable the CHG/DSG FETs if they are appropriately configured in fully autonomous mode with the corresponding fault protections enabled for each FET.

  • 0 in reply to Gavin Long
    Intellectual 425 points

    Hi Gavin,

    Thank you for your reply. Please also help me with the following questions，Thanks.

    1. Do the DSG and CSG MOS transistors have other functions besides current protection?
    2. Can the DSG and CSG MOS transistors be removed, and can the customer use an external Pack+Pack- for power protection?
    3. Does the BQ76907's VSS terminal need to be connected to the negative terminal of the battery?
    4. What are the functions of capacitors C20 and C21, and are there any requirements for their selection?

  • 0 in reply to Alon Chen
    TI__Intellectual 880 points

    Hi Alon,

    Below are my responses to your individual questions:

    Alon Chen said:
    1. Do the DSG and CSG MOS transistors have other functions besides current protection?

    Besides the overcurrent/short-circuit protection during Charging or Discharging, they also will disconnect from a Charger/Load in reaction to a cell’s over/under voltage, TS over/under temperature, internal overtemperature, host watchdog timeout, and VREF/VSS/REGOUT measurement check. These faults can be configured to turn off the FETs using the CHG/DSG FET Protections A and Both FET Protections B Registers. Finally, the FETs can also be manually turned off using host commands if desired

    Alon Chen said:
    2. Can the DSG and CSG MOS transistors be removed, and can the customer use an external Pack+Pack- for power protection?

    Yes the CHG/DSG FETs can be removed entirely, if you choose to use a separate Pack+/Pack- protection. If this feature is not needed then the CHG/DSG pins can be left floating.

    Alon Chen said:
    3. Does the BQ76907's VSS terminal need to be connected to the negative terminal of the battery?

    Yes, the VSS terminal needs a low resistance path to BAT- terminal that bypasses the VC0 series resistor.

    Alon Chen said:
    4. What are the functions of capacitors C20 and C21, and are there any requirements for their selection?

    The capacitors (C20, C21, C14, & C18) are known as ESD capacitors. These provide a path for current to flow in case of an ESD event that bypasses both the FETs and battery. Two capacitors are put in series as an additional safety measure so that if one capacitor fails, there is not be a short circuit path between the two paths.