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BQ76942: Current shunt resistor value for up to 50A normal use?

Richard Cooke
Expert 1530 points
Part Number: BQ76942

Hello,

What is the recommended shunt value for an application that can handle up to 50A from an 8S LiFePO4 battery pack?  To keep the voltage below the 200mV limit I can use 4mOhms but the resistor would have to handle 10W.  If I use two 8mOhm in parallel they would only have to handle 5W each.

In the BQ76942 datasheet section 18 (page 75) under Layout Guidelines the following statement has me concerned: " The device is designed to support a 1-mΩ sense resistor."  Is it reasonable to use a 4mOhm sense resistor?

Thanks,

Richard

  • 0
    TI__Prodigy 720 points

    Hi Richard,

    Yes, 4mOhm sense resistor is viable (as well as other resistors greater than 1mOhm). Although, this would put you close to the dynamic voltage range limit of 200mV (at your max of 50A). So, a suggestion would be to reduce the size of the sense resistor (at 3mOhm and 50A you would reach a safer 150mV and 7.5W of dissipation).

    Hope this helps.

    Best,

    Andrew