I have built a buck converter on the TS30011. Unfortunately, I am getting terrible noise on the output.
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I have been analyzing my design and have been getting awful results. 
My low-frequency noise is not terrible, but I am being plagued by the high-frequency noise. I have noticed two immediate errors with my design.
1) I did not separate the analog ground and the power ground as it says in the datasheet. Apparently it is only supposed to be connected at a single point, but I did not do this.
2) I must add bypass capacitors at the input of the device as close as possible.
I am hoping that these two issues alone will make my device usable, but I am wondering if there are any other suggestions for removing high-frequency noise from a buck converter.
I saw that a capacitor multiplier circuit could be used to smooth out the signal. Is this a good way of adding additional filtering? Any other suggestions would be greatly appreciated! 
Answer
Input filtering is a must. In addition to that I find it a must to use at least a full GND plane when dealing with switching regulators. Along with a full GND plane you can have much better routing for the other power connections.
Some additional things to go along with that:
- Use every effort to keep all of the VSW connections as clustered together and as small as possible. Best is to have no vias on VSW.
- Use a cutout under the VSW node and associated pads in the GND plane and any other power planes. This helps eliminate coupling into the power and GND planes.
- Do not route any other signals through the VSW area on any layer. This node handles the highest ripple current at high frequency and can couple to other circuits very easily.
- Try to design your board layout so that the switcher layout is not compromised in any way. Trying to place mounting holes and non-related connectors nearby is a compromise.
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