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setting bq20z40 overcurrent

Timothy Starr
Expert 2445 points
Other Parts Discussed in Thread: BQ20Z40-R1, BQ29330

For the bq20z40-r1 eval board, the parameter AFE SC Dsg Cfg is set in 25mV increments. How does this relate to the actual overcurrent thrsehold in amperes? Some kind of conversion ratio is required, but can't be found in the documentation. Thanks!

  • 0
    TI__Genius 10235 points

    The value relates to the sense resistor.  You need to divide the value of the register by your sense resistor value. This will give you the current threshold.

  • 0 in reply to Chase7071949597
    Expert 2445 points

    So, for the Evaluation Board, the sense resistor is 10 milliOhms. a 25mV step represents 2.5A? That means the default value of discharge current limit is 297.5A (hex 77) and the amximum is 637.5A (hex FF). This seesm awfully high/course. Can you confirm please? Thanks!

  • 0 in reply to Timothy Starr
    TI__Genius 10235 points

    Actually, the register contains both a timer and threshold for setting the current.  The high nibble is the timer setting, which determines the delay before the FET is turned off. The bq29330 datasheet shows the table for the timer settings. The lower nibble is the current threshold. So, the default threshold is actually 07, which indicats a default of 17.5A for a 10mOhm sense resistor.