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BQ76200: Gate oscillation resistor

Criton Kallkkaran
Prodigy 105 points
Part Number: BQ76200
Other Parts Discussed in Thread: BQ76952

Tool/software:

Hi Team,

I am trying to understand the use of BQ76200 with multiple charge and discharge FETS. I have a few questions regarding it.

1) From the attached image, after reading the FET drivers my understanding the resistor/inductor is on the gate of the CHG/DSG MOSFETS are used to avoid oscillations. How do you choose the value of resistance for a MOSFET of different choice?

2) Also after reading the application note from BQ76952 Multiple FETs with the BQ76952, BQ76942 Battery Monitors (Rev. A) the resistor/ inductor used at the Gate of the MOSFET is 51ohm (please see the attached image). Could you please explain the choice of these values?

Many thanks and Kid regards,
Criton


 

  • 0
    TI__Mastermind 42060 points

    Hello Criton,

    Criton Kallkkaran said:
    1) From the attached image, after reading the FET drivers my understanding the resistor/inductor is on the gate of the CHG/DSG MOSFETS are used to avoid oscillations. How do you choose the value of resistance for a MOSFET of different choice?

    There is no defined best way to choose this. When this is described in  industry literature, it is often recommended to use a small individual gate resistance of at least 10% of the total resistance or a ferrite bead to isolate the gates to suppress the oscillation.

    We have used 10-Ohms to 100-Ohms in these types of FET driving systems. The higher the individual gate resistance it is, the less likely oscillations is to occur, but the more delay it will add the the switching speed.

    Criton Kallkkaran said:
    2) Also after reading the application note from BQ76952 Multiple FETs with the BQ76952, BQ76942 Battery Monitors (Rev. A) the resistor/ inductor used at the Gate of the MOSFET is 51ohm (please see the attached image). Could you please explain the choice of these values?

    Not any particular reason that I know of. The following E2E post may also be useful here:

    e2e.ti.com/.../3900591

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 105 points

    Hi Luis,

    Many thanks for getting in touch. 

    Luis H. S. said:
    There is no defined best way to choose this. When this is described in  industry literature, it is often recommended to use a small individual gate resistance of at least 10% of the total resistance or a ferrite bead to isolate the gates to suppress the oscillation.

    Could you please clarify if its 10%of total resistance of the parallel mosfets that are connected? 

    Many thanks,
    Criton

  • +1 in reply to Criton Kallkkaran
    TI__Mastermind 42060 points

    Hello Critton,

    This typically means the resistance of your driver. I have seen some documents say 20% of the load current, other 10%. There are no defined rules for it. 

    Best Regards,

    Luis Hernandez Salomon