TPS53353: Ripple injection

christopher2

Part Number: TPS53353

I have two DC/DC converters based on TPS53353. They both work set to 3,6V, both are identical, same components.

No I am wondering why the ramp(lower picture) which I inject to the VFB pin is a little different in one converter, they both are around 50mV.

Question is why: one sawtooth is let say not "ideal"?

They are both with noise and spikes I see but why the ramp is not continuous, we can observe a big drop around the peak.
I reduced the amplitude even to 30mV, so that's not the reason. The first picture is with a good Ramp

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

When you see an offset like that, it is indicative of series inductance. Do you have a high ESL component or long, thin trace in the signal path? Are both PCB layouts exactly the same?

0 christopher2 over 7 years ago in reply to JohnTucker

Intellectual 515 points

Placement is the same, tracks the same, entire layout was cloned. There are only some small differences with vias to ground plane around inductor.

Seems its layout related.
Any possible solution, to fix this offset? better grounding, some extra caps?

0 JohnTucker over 7 years ago in reply to christopher2

TI__Guru**** 191445 points

The stray inductance could just as easily by in the ground path as the signal path, so that is possible. It may also be due to measurement technique. Can you re-measure your ramp signals with a very short (< 1cm) ground lead on your probe? I typically remove the plastic barrel cover and wrap a short "pig tail" of bus wire around the exposed ground barrel.