Electronic – Half-Bridge Gate Driver Circuit Question

mosfet-driver

I got two questions about Half-Bridge Gate Driver MP1907 circuit on brushless motor driving.

  1. MP1907 chip's eveluation board uses 1uF for bootstrap capacitor. However the 20A brushless motor ESC i have uses 4.7uF. Does the value matter?
    Should I use a smaller value like 1uF for fast charging in fast switching applications?
    The application is brushless motor driving around 20-30A max current. The voltage is around 16V.

  2. The ESC I have uses 47 Ω resistor between gate of the MOSFET and the DRVH, DRVL pins of the MP1907. Is this necessary? What good is in there to use them since again eveluation board does not use any resistor and connects the Drive pins of the MP1907 to gate of MOSFET directly?

MP1907

Best Answer

  1. The boost capacitor needs to be large enough to be able to supply the gate charge required by the high-side MOSFET on every switching cycle without significant voltage droop. A small capacitor might charge quickly, but it discharges quickly, too.

    Generally speaking, the boost capacitor should be at least 10× to 100× the effective gate capacitance of the MOSFET, but 47µF sounds excessive to me.

  2. The gate resistor helps to suppress parasitic oscillations at VHF frequencies that can occur with large MOSFETs (gate-to-drain capacitance resonating with the parasitic inductance of the gate connection), which is important both for efficiency and for EMC. It should be mounted as physically close to the transistor as possible.

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