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BQ76920: What is the side effect if floating VC5 in 4cell application.

Jeff Chen71
Expert 1345 points
Part Number: BQ76920

Hi ,

     Customer didn't follow the datasheet  section 11.1.1 Configuring Alternative Cell Counts to draw schematic, they were floating vc5 as bellow picture.

Because they didn't found any problem and work well ,so they would like to know what is the side effect if they float the vc5.

Thanks 

  • 0
    TI__Guru 54715 points
    Hi Jeff,
    VC5 is an input and should be connected. Practically the cell 5 has an internal balance FET and the body diode will prevent the pin from falling significantly, but the long term effect of operating with the input floating is not known.
    The bq76920 should be operated with the top cell used as shown in seciton 8 of the data sheet. The VC5 is better able to handle common mode variations to the BAT pin than other VCn pins. Using cell 4 at the top may lead to variation in the top cell accuracy as BAT varies. In the schematic shown REGOUT does not show a destination so variation from its load change may be small.
    The VCn pins should be used with a filter to the cell connections which is not shown in this schematic segment.