Hello,
I recently designed a board using the LM5163 as a first step in the DC/DC conversion from the input voltage of 40-80V. It takes it down to 12V, and then I have a 12V/5V and a 5V/3.3V converter on board as well.
I am applying 48V from an AC/DC power supply and using a breaker switch to let power go to my board (after the AC/DC supply is already turned on).
When I flip the switch, I can see on my 5V and 3.3V lines some nasty transient spikes that go both positive and negative. This is before the LM5163 even starts working, I think.
Is there any way you guys can help me to find out if the LM5163 chip or layout is causing this, or if my layout is bad somehow? I can share schematics and PCB files upon request, but what I wanted to show is this transient I recorded on the scope on the 5V line shortly after power up. 
I think these transients killed my microcontroller because it was working the first few power-ups, but eventually it started to heat up instantly. It has a negative input rating of only about -0.3V, so I think the transients I'm seeing are much worse than that.
Is this expected behavior when hard switching on power to the device with a physical switch?
If so, is there a good way to stop this? I tried lots of different capacitors and filtering strategies, and RC snubbers, etc., but I can't seem to get rid of this. I'm not sure if this just happens and it's so transient that it's not important, but hoping to figure out more about it.
