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TPS56121: TPS56121 design noise

Part Number: TPS56121
Other Parts Discussed in Thread: TPS56221

Dear Power Design Expert,

I have a design with TPS56121. the parameters are from Webench, it is a 12V input, 9V, 9A output.

it is used to drive a TEC, the R125 will be set to 2.8V or 0.48V to control the output voltage to 1.6v or 8.5V.

the board is 4 layers. one full ground layer. The board can output the correct voltage and current without a problem, but for some reason, it causes the system overall noise level to rise. after some measurement, I notice that the input cap has very high transaction noise as in the following waveform.  I attached the waveform, schematic, and layout. for this kind of problem, is there a general rule to troubleshoot. for example, is the components value, placement, layout trace should be paid attention, how to design the next test to improve the design? where should I start to respin the board?

high current power regulator is not easy to design. hope I can get some suggestion, appreciate your help.

The high lighted area is the 12V input to the U56