A Novel Method to Reduce Effect of Negative Gate Voltage Spike and Oscillation to Protect Gate Driver

Motor control unit frequently employ high power devices such as Si MOSFETs and controlled by voltage from the gate driver. Gate drivers are more critical to provide enough source, sink currents and there by controlling the gate voltage of Si MOSFET. During dv/dt, di/dt variations and due to track or lead inductances of Si MOSFET the switching node which is the midpoint of half bridge consists of high negative gate voltage spike and oscillations, this may cross the gate driver pin voltage limits. The gate driver safety and normal operation is the key for driving the motor with motor control unit. The oscillations at gate voltage may impact on system electromagnetic emissions. This paper presents about suppressing the gate negative spike voltage during turn-off process. A novel method is presented with addition of decoupling capacitor between the switching node and supply ground to reduce the effect caused by trace or lead inductance of Si MOSFET and its interaction with internal capacitance, thereby protecting the gate driver without failure. Design analysis, simulation verification and experimental validations are implemented to demonstrate the effectiveness of proposed method. The novel method with addition of decoupling capacitor helps in protecting the gate driver successfully by suppressing the Si MOSFET's negative gate voltage spike and oscillation.