TPS54388-Q1 PH waveform

Hello,

Looking at the waveforms, it looks like you may have some measurement issues or layout related issues.

Can you please check the following?

* Measure the SW waveform very close to SW pin with very short connection to oscilloscope probe tip and GND of oscilloscope probe should have very short connection to the regulator GND. Measurement set up should be something similar to ripple measurement specified in the below link, but between SW pin and GND pin instead of between the Vout and GND in the case of ripple measurements.

https://e2e.ti.com/support/power_management/simple_switcher/w/simple_switcher_wiki/2243.understanding-measuring-and-reducing-output-voltage-ripple

* If the problem is still not solved, please check by adding a RC snubber circuit at the SW node.

* Also send me the schematics and layout diagram for the review.

Regards,

Murthy

Murthy-san
Thank you for your reply.
I talked with customer for checking of your suggestion.
They think they don't have measurement issues.
PH: PIN10,11,12 direct
GND:PIN3,4 direct

Could you give us your comment for
"Does this waveform cause any problem or does this wave form destroy this IC?"

Kura-san,

If it really violates ABS max ratings, I cannot really say whether this will destroy this IC. Even if it looks ok on few devices, we cannot tell what will happen across devices and lots and also over life time of the device. Lets try to focus on solving this issue. May be it is some layout or schematic related, if it is not measurement related.

Regards,

Murthy

Murthy-san

Thank you for your reply.

I checked TPS54388EVM and found same PH waveforms.

Please checked attached.Load is 2A and 3A.

When load level is increased, ringing voltage level become large.Ringing time is almost same.

Ringing time is long.

http://www.tij.co.jp/jp/lit/ug/slvu962/slvu962.pdf

probe:TDP1000 (We used FET probe)

oscilloscope:DPO7254

TPS54388EVM

www.tij.co.jp/.../slvu962.pdf

Same waveforms are found on EVM,So we need that  your comment that customer's waveforms are acceptable.

Murthy-san

There is additional information.

I attached their probe information.Please give us your comment.

 

Hello Kura-san,

It is difficult to say whether this probe set up is still good enough or not. They have to try it out. Also they have to measure directly at the IC pin. For example, i used the attached probe set-up.

In my opinion, it should be fine for the IC. This is an old device and used by many customers and we did not receive any complaints for the field so far on this issue.

Regards,

Murthy

PH.xlsxFor more understanding,I re-attached  customer waveform.

Please re-check attached.

Time period below -0.6V is from 4ns to 9ns.Please give us your comment.

In my opinion, it should be ok.