Synchronous Buck Converter High Side Gate Voltage Ringing

Thread Starter

ALİHANATAY

Joined Dec 14, 2020
5
Hello everyone,
I prepared the buck converter design, whose schematic I have shared below. After preparing the PCB and starting the testing process, huge ringing occur in the high side Mosfet's Gate Voltage. My switching frequency is 150kHz. The wave shown in yellow indicates the High side Mosfet Gate Voltage. The blue one is the low side mosfet gate voltage. This ringing also greatly affects the Drain-Source voltage. Can you help me on this topic?
Thanks.

tek00014.png

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Delta Prime

Joined Nov 15, 2019
1,160
Hello there :) When turning on the mosfet, (it begins to conduct) Vds drops very quickly and that causes the charge in Cgd (aka Crss or feedback capacitance) to get dumped into Cgs which fights the gate driver and forces Vgs toward zero tending to momentarily turn the mosfet back off. You can mitigate this effect by adding capacitance between the gate and source. This will have a twofold effect, first it will make Vgs less sensitive to the charge dump from Cgd and second it will tend to reduce the dV/dt of Vds lessening the impact of inductance between the gate driver and the gate
 

Thread Starter

ALİHANATAY

Joined Dec 14, 2020
5
Hello there :) When turning on the mosfet, (it begins to conduct) Vds drops very quickly and that causes the charge in Cgd (aka Crss or feedback capacitance) to get dumped into Cgs which fights the gate driver and forces Vgs toward zero tending to momentarily turn the mosfet back off. You can mitigate this effect by adding capacitance between the gate and source. This will have a twofold effect, first it will make Vgs less sensitive to the charge dump from Cgd and second it will tend to reduce the dV/dt of Vds lessening the impact of inductance between the gate driver and the gate
Hello,
Thank you for your answer. I will try adding capacitance, I let you know if it works.
 

Thread Starter

ALİHANATAY

Joined Dec 14, 2020
5
Hello,
Thank you for your answer. I will try adding capacitance, I let you know if it works.
Hello,
This solution is cause slow discharging high side mosfet gate source voltage. Therefore High side mosfet closes late and increase losses. Do you think we can solve this problem by adding a snubber circuit to the Low side mosfet.
 
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