I have a strange problem with the MOSFET Push-Pull configuration of an output stage of a simple buck converter.
On the falling edge of the Low-Side MOSFET I get an effect like ringing, but it is actually following the rising edge of the other MOSFET. What can it be? Can it be caused by stray inductance and the current of the High-Side MOSFET induces some into the gate of the Low-Side MOSFET?
I will include three pictures. One with the circuit, one with the PCB (Some explanations under the picture) and the last one with the problem.
Schematic:
PCB:
The green trace is carrying the Low-Side MOSFET signal and it goes right under the pin where the High-Side MOSFET signal is outputed from the IR2011 (MOSFET driver). Could this be the problem?
Oscillogram of the MOSFET driving signals (blue – Low-Side, yellow – High-Side):
Best Answer
When the high side FET starts to turn on, the switch node rises rapidly. This dV/dt causes a current in the gate-drain capacitance of the low side FET. This current tends to pull up on the low side FET gate, and can ring with the stray inductance.