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I have built a buck converter on the TS30011. Unfortunately, I am getting terrible noise on the output.

enter image description here enter image description here

External Parts Used:

Inductor

Output Capacitors

I have been analyzing my design and have been getting awful results. enter image description here

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! enter image description here

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  • \$\begingroup\$ THe spikes look like >20MHz Probe ground ESL resonance with 10:1 coax capacitance. Search site for best practice to measure CM and DM SMPS noise with < 1cm spring clips only. Then compute using 1nH/mm and probe ca[acitance with Cap ESR * load current for ground shift. Best Practice for me is AC couple to 50 Ohm coax and terminate with 50 Ohms at DSO using semi-rigid cable,but use what you have \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 16 at 5:38
  • \$\begingroup\$ The schematic doesn't make clear whether or not you have input capacitors before the Buck converter. If you don't, please add. They need to be as close as possible to the controller. \$\endgroup\$ – joribama Oct 16 at 5:43
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    \$\begingroup\$ You appear not to have followed the example layout in the datasheet. Now you have long loops through which current spikes flow. You MUST keep the loops small and use thick traces like shown in the example. Even if you used all the right components you can destroy the circuit's performance by having a "crappy" PCB layout. \$\endgroup\$ – Bimpelrekkie Oct 16 at 6:26
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    \$\begingroup\$ Show probe setup. \$\endgroup\$ – winny Oct 16 at 7:07
  • \$\begingroup\$ As mentioned, you need to keep the layout tight around the converter. A GND plane would help. Personally I would choose a better output capacitor. I never use X5R (X7R costs the same) and always use capacitors rated for at least twice the voltage across them. Look at your capacitors datasheet. The DC bias characteristics chart shows that the capacity has dropped 75% at 5V. It is hard to find a good high capacity ceramic capacitor rated to more than a few volts. You might be better of with a combination of a bulk electrolytic or tantalum capacitor with a few lower value ceramic capacitors. \$\endgroup\$ – Peter Karlsen Oct 16 at 8:40
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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:

  1. 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.
  2. 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.
  3. 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.
  4. 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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