I have developed a 48v -> 6v DCDC switching regulator using the [LTC3810](http://cds.linear.com/docs/Datasheet/3810fc.pdf). It works well, except that there is some ringing on the output at each switch. You can see the 'scope trace on the picture. This measurement was taken across the input cap of the 3.3v regulator, approximately 30cm of wire away. I get one of these every 4us (250kHz). The amplitude looks to be about 200mv p-p. The ringing is bad enough to go right through the next regulator (another DCDC 6v -> 3.3v) and is causing problems with my EtherCAT transmission. 

What is the best thing to do about this? Should I try adding a little inductor or a resistor somewhere at the output? I already have a pretty massive output cap (5600uF).

Added:

I have tried adding ferrite beads, inductors and caps as suggested, but they did not help. I'm now trying a larger main inductor.

![Switching ring on LTC3810 circuit.](https://i.stack.imgur.com/jtNM4.png)
![LTC3810 circuit](https://i.stack.imgur.com/Szv8X.png)
![Render Bottom Side](https://i.stack.imgur.com/muIaa.png)
![Render Top Side](https://i.stack.imgur.com/9q1VA.png)
![enter image description here](https://i.stack.imgur.com/atDpm.png)
![Power supply layers](https://i.stack.imgur.com/WI0az.png)