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BQ76940: Bq76940 Fet Gate Driver

Ansul Tyagi
Intellectual 305 points
Part Number: BQ76940
Other Parts Discussed in Thread: UCC27524

Hi,

I'm using Bq76940 and 24 MOSFETs for charge and discharge protection (12 parallel for CHG and DSG each). I would like to drive these MOSFETs using a gate drive IC.

Are there any recommended parts for gate driver IC? or any circuit or document?

I want to use low side switching

  • 0
    TI__Guru 54715 points

    Hi Ansul,

    I'm not aware of a document.  Using an external driver for a large number of FETs is a good idea since the drive from the BQ76940 is limited.  In general you will need a power supply for the driver and to lower the control voltage to the inputs if needed.  Remember that the charge FET can go  below BAT-.

    You might consider the UCC27524 with a P-ch FET in the path for the charge gates if the passive turn off of the charge FET is acceptable.  If you want to drive the charge FET off when it is below BAT- consider a single channel low side driver for the DSG and an isolated gate driver for CHG, with an isolated power supply.  For more information on gate drivers see http://www.ti.com/gatedrivers 

  • 0 in reply to WM5295
    Intellectual 305 points

    Hi WM5295,

    Thanks for the information.

    referring to document slua749, there is CHG_CLAMP Zener diode inside the BQ76940 AFE. this will protect CHG pin from BAT+ voltage.

    How can we protect UCC27524 output pin from BAT+ voltage?

    I have thought of a simple circuit on the lines of slua749 document.

     

    Let me know if this can work

  • 0 in reply to Ansul Tyagi
    TI__Guru 54715 points

    Hi Ansul,

    Yes I think that can work.  To reduce 1 resistor you may be able to move the zener to the driver OUT pin with a voltage above the normal OUT voltage but below the P-ch FET Vgs maximum.

  • 0 in reply to WM5295
    Intellectual 305 points

    Hi WM5295,

    UCC27524 datasheet says that maximum voltage at driver OUT can be VDD+0.3 

    that means for 12V system, driver OUT can have maximum voltage of 12.3V.

    And the output voltage will also be around 12V. It is difficult to select/control a Zener diode between 12V and 12.3V.

    is my understanding of UCC27524 correct?

  • 0 in reply to Ansul Tyagi
    TI__Guru 54715 points

    Hi Ansul,

    Good point, thank you!  I'm not the expert on gate drivers.  OUT's abs max is based on VDD applied, not on maximum allowed VDD.  Your circuit better addresses the limitations and tradeoffs.