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how to choose external MOSFET gate resistance with UCC27211DDA gate drive is used?

Leonardo Callegaro
Expert 1605 points
Other Parts Discussed in Thread: UCC27211

Hi all,

I am quite new in this area and I have a couple of questions.

1) Do you know how do you choose the gate resistance for a MOSFET when the Texas instruments UCC27211DDA gate driver is used? I am using the MOSFET (150V, 100A) as per table below, in my design for a dc-dc converter. The mosfet gate will be connected (via the external resistance whose value I need to choose), to the gate driver PIN HO. Also, the MOSFET switching frequency will be 200kHz.

2) what is the voltage coming out of the UCC27211 pin HO? (this will be the PIN connected to the gate driver via the external resistor)

PS below is the MOSFET data:

Datasheets

IPB072N15N3 G

Product Photos

TO-263

Family

FETs - Single

FET Type

MOSFET N-Channel, Metal Oxide

FET Feature

Standard

Drain to Source Voltage (Vdss)

150V

Current - Continuous Drain (Id) @ 25°C

100A (Tc)

Rds On (Max) @ Id, Vgs

7.2 mOhm @ 100A, 10V

Vgs(th) (Max) @ Id

4V @ 270µA

Gate Charge (Qg) @ Vgs

93nC @ 10V

Input Capacitance (Ciss) @ Vds

5470pF @ 75V

Power - Max

300W

Thank you so much,

Leonardo

  • 0
    TI__Genius 9130 points
    Leonardo,

    The value of the gate resistor depends on your system requirements, i.e. how fast you want or need to switch the FET on and off. A smaller value gate resistor will make the switching speed faster, and should improve efficiency, but may increase EMI. It really depends on your application and the topology. If it's soft-switching, then EMI will be less of an issue and you can switch the FET really fast.

    You will probably need to tune the gate resistor in the system, but as a start you could use maybe 10 to 20 ohms, since it looks like the FET is pretty hefty. Again depending on your topology, quite often a separate turn off path is provided using a diode in series with a smaller value resistor, to get asymmetric turn on/off speeds. Often, fast turn-off is more important.

    Finally, be careful that you use the right type of resistor. It should be sized to handle the required continuous power (P = fQV where f is the switching freq, Q is total gate charge, V is the driving voltage). Some of this power is dissipated inside the driver IC, and some in the external resistor, in proportion of the external and internal resistance. So a larger external resistor value will result in more power in that resistor, and less inside the IC. You should also be sure that the chosen resistor type can handle the peak pulse currents, which will be V/(Rint+Rext). The high pulse currents can affect the long term reliability of the resistor. and again, smaller external Rext will lead to higher pulse currents.

    The voltage at the HO pin will be approx. the same as the VDD level, it will be slightly less due to the drop across the bootstrap diode.

    I hope this answers your questions.

    Thanks,
    Bernard