I am using a TPS54320 to step down a 12V input to 1.9V with a 1A nominal load. I am seeing some variation on the switch node / inductor current as shown on the attached images.
The design has been verified with the TI software and the voltage feedback loop was validated to have ~55 Phase margin with a 1A load as shown on the attached image.
My understanding is given the duty cycle we are operating at, we should not be seeing sub-harmonic oscillation so I am not sure what is going on.
I want to note that we have seen this behavior before and we had to play with compensation and inductor values to make it go away.
We can certainly try that strategy again, but we would like to understand this behavior so we can properly address it at design time and feel confident shipping the design.
Here is the schematic for this part:
Phase Margin for the above circuit (consistent with what I calculated/simulated)
Inductor current with constant 1A load applied (scope has 1A offset applied)
1st capture:
Different capture, but nothing changed with respect to above (i.e. still 1A, just re-trigger scope):
Zoom out and re-capture, again same setup:
Now, drop the current to 0A (no load) and re-capture the inductor current:
And a zoomed out version with no load current:
Thank you for your help,
