TPS54318 PH pin overshoot

Hello - Thank you for your interest. 

Could you show a waveform which has max ringing greater than 7V? 

Measuring ringing on PH can be tricky. Any inductance from the probe to ground (such as the ground clip), will exaggerate the ringing and show a much higher spike than actually exists. To properly measure ringing on PH you'll need to measure with a very small ground lead (just enough to reach from the PH pins of the device to the PGND pins). This will reduce the artificial pickup from the long ground lead. 

Thank you for your answer.

I have observed the waveform by using GND spring. At that time, I observed 7.4V overshoot.

But this time, I connect the probe to TP2 of EVM for GND and TP3 of EVM for PH directly.

So the overshoot reduce to 6.84V.

I will attach the waveform.

6724.TEK00008.TIF

But my customer worries about the margin up until maxiumum rating.

They want information for making a decision that TPS54318 doesn't break in consideration of the temperature change, the part variation.

Even the extra inductance added by the plane/traces from the pins to the traces to the test point, and the long ground lead on the scope will still exaggerate the spike level seen. We're trying to measure a very high frequency effect here, so standard probing techniques may be a little misleading. 

I would recommend using a common HF probing technique, where the the probe tip is put right up against the PH pin, and the ground length is minimized by wrapping a length of bus wire around the scope barrel (which is grounded), and having just the end of that wire meet the GND pins of the device.