TPS62A01: Switching Node at Light Load

Hello Frederic,

Thank you for reaching out,

Can you please provide me your layout?

Can you please share me how you are measuring the switch node voltage? I would recommend to use pig tail method or tip and barrel method to measure the SW node voltage. (+) How to measure ripple for better design outcomes - Power management - Technical articles - TI E2E support forums

Some times the long wire of the probe acts as a antenna and leads to this kind of high amplitude ringing.

Fred P said:

the absolute maximum value of the SW pin (VIN+0.3).

This should not be any problem if the device is in PSM mode.

Fred P said:

I'm not used to see such ringing in DCM. Since it busts the absolute max, I guess I no choice but to add a snubber...  That's one problem.

Generally there is no necessity to add the snubber, if the layout is good.

Thank you & regards,

Moheddin.

Below is the layout snapshot.  3VX is the output. SYS_PWR is the input.  SW is the switching node.

I'm probing with a little spring as always.  That would be the pigtail method from your link.

Probe contact points are indicated by yellow arrows.

Blue dashed line is feedback trace on bottom layer.

In between, there are 2 signal layers (nothing routed nearby) + full GND plane + full power plane.

As for the snubber, indeed, I never had to add any because of DCM ringing!  As a matter of fact, I never had to add any for tens of low power DC-DC.

Please also advise on switching pattern and the downslope.  Look like some good opportunity to learn here....

Thanks

Fred

Thanks for the explanations.

As for the overshoots, since the layout is ok, you think they are much lower than what the probe picks up?

Nothing to worry about here?