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BQ76920: Can Charge and Discharge mosfets be connected common source?

FJ
Intellectual 360 points
Part Number: BQ76920

1) Is it possible to connect CHG and DIS mosfets in common source configuration?  Do you have any reference designs with common source connection?

2)  Can Rsns resistor be located across common Source?

In my application I am using To220 style fets.  The Drains will be bolted to bus bars that connect to the battery and pack - terminal.  The Source pins on the fets are connected via a separate PCB that is copper filled. On this PCB I would like to place the RSNS resistors.

  • 0
    TI__Guru 54715 points

    Hi FJ,

    1. We do not have any reference designs with the FETs in a common source configuration.   With the common drain configuration the discharge FET gate which supports switching of the discharge current, typically the higher current in a battery system moves over a 0 to 12V type range for off to on.  The charge FET gate must move over a range of some large negative voltage (charger greater than battery voltage, discharged battery with fault and FET off) to PACK+ or greater (discharge FET off with load and/or transient), but when on is also at some ON voltage for the FET of about 12V.  With common source FETs the charge FET gate would have a reduced range but still go negative, the discharge FET gate would have a much larger range and still need to turn off quickly.  With isolated drivers a common source configuration should be possible, but the drivers are more complex.

    2. The BQ76920 can not support the sense resistor in the common source path of the FETs.  The recommended operational range of SRP is +/- 10 mV.  ABS MAX for both SRP and SRN goes to -0.3V.  The SRP and SRN inputs would likely be damaged if a charger were connected without the charge FET on.