Hi,
I have a design with LM5005. Here are the main parameters:
Vin=48V
Vout=12V
Switching Freq=387kHz
Scope picture at swithing node:
My problem is that there is a huge high frequency noise at the switching node which cause issues at the other side of PCB. The overshoot is nearly 25V and the ringing frequency is around 134MHz. According to the datasheet and the EVM the common solution is to place a snubber circuit across the power diode. I tried it and it reduced the ringing, but the overshot and the first few period of the ringing remained.
Switching node with snubber:
My next experiment was to place a resistor in series with the boost capacitor. It seems to work much better now, however I have some concerns with this method. Are there any downside of this method?
Are there other possible solution to reduce the high frequency noise? In the PCB the input caps are as close as possible to the VIN pins.
Regards,
Tibor