A signal generator giving out 32Khz pwm waveform input to OC1A which powers discharge FET, comparator etc…. You can see there is a lot of ringing at turn on and turn off; the gate is going to -1V.

Figure 1: 32khz waveform applied to the OC1A

Here you can see the rise time on the FET with respect to the input PWM. The FET has Vgsth = 4V. Look at the curve; it takes close to 400ns to reach the 10V which will allow the FET to be in the minimum Rdson state. Ideally the FET should be ON within 50ns to 80ns for minimum losses.

This part is the hysteresis of the comparator/opamp

Figure 2: Rise time on the FET gate (400ns rise time causes FET to be in linear mode for longer time)

Here you can see the fall time on the FET with respect to the input PWM. It takes close to 1us to reach the 0V which will allow the FET to be in the off state.

This part is the hysteresis of the comparator/opamp

Figure 3: Fall time on the FET gate (1us causing FET to be in linear mode for longer time)

The same 32khz waveform this time thru a lowside FET driver (TC4424). You can notice that there is no ringing on the turn on or turn off.

Figure 4: 32khz PWM signal thru a lowside FET driver (TC4424)

Very clean switching waveform when using the FET driver. Switches FET from Off to On in 50ns. This is the Miller Plateau zone of the FET. The FET driver is providing increased current to overcome the capacitance.

Figure 5: FET switch On thru TC4424 driver

Again clean turn off waveform. Switches the FET from On to Off within 40ns.

Figure 6: FET switch Off thru TC4424 driver

CONCLUSION: USE DEDICATED FET DRIVERS IF YOU WANT THE MOSFET TO LIVE AND PROVIDE RELIABLE FUNCTIONALITY.