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BQ76940: I want to use BQ7640 low side driver multiple FETS

user6501051
Intellectual 685 points
Part Number: BQ76940
Other Parts Discussed in Thread: UCC27524

Currently i have one project use BQ76940 to low side drive multiple fets, but the BQ76940 insufficient driving capacity, so it needs one low-side driver to drive multiple FETs, i want to use two Bipolar Totem-Pole Driver,  one connect DSG pin, another connect CHG pin, I don't know if it's feasible. Does TI have recommendations for low-side drivers that can be used

  • 0
    TI__Guru 54715 points

    Hi User,

    The BQ76940 has low side drivers built in, but the part has internal resistance and some external resistance should be used which will limit the speed for large FET arrays.  A circuit such as you have pictured is helpful to return the current close to the FETs or provide lower resistance for larger FET arrays.  The charge FET is more challenging due to the range of voltage over which the gate must move. Allowing a negative voltage is often provided in a battery with a P-ch FET and the high voltage blocked from the driver using a diode.  This can make charge turn off slow, so a circuit to aid turn off or an isolated driver may be more attractive for large charge FET arrays.  While it was focused on another monitor family the application report  https://www.ti.com/lit/pdf/sluaa84 showed a couple external driver driver options for low side switching in a battery and may provide useful guidance in your investigation and selection.  The UCC27524 was used for testing in that application report, other driver options can be found at www.ti.com/gatedrivers .  The BQ76940 DSG and CHG provide a signal from 0V to about 12V, see the data sheet, these should be good as inputs to drivers, but always check the driver data sheet for suitable input ranges.