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3 months ago in Power Electronics By Krirthi

What does "ring back" mean in a pwm controller datasheet?

I'm designing a DC-DC converter and studying the switching node behavior on the oscilloscope. The datasheet mentions minimizing "ring back" for better performance, but the term isn't clearly defined. I understand ringing from parasitic inductance and capacitance, but is "ring back" something distinct, or just industry jargon for a specific part of that ringing waveform I should be paying attention to?

All Answers (2 Answers In All)

By Raghu Answered 1 month ago

"Ring back" refers to unwanted oscillations or ringing in the feedback signal (voltage or current sense) after a rapid transient. Imagine a sharp step instead of settling cleanly, the signal bounces. This parasitic ringing can cause false triggering, instability, and degraded performance. It's usually caused by parasitic inductance and capacitance in the PCB layout or sense circuit. The fix: careful layout, proper damping, and sometimes a small RC snubber. The datasheet warns you: if you see ringing, don't ignore it. It's not noise; it's a problem.

                             

By Mark Answered 3 weeks ago

From years of power supply design, I can clarify this. Ring back specifically refers to the negative undershoot portion of the switching node waveform that goes below ground after the initial ringing. It's not just aesthetic this negative voltage spike can forward-bias the body diode of your synchronous rectifier or cause substrate injection in the controller IC itself. I have seen designs where excessive ring back led to erratic operation or even latch-up. The datasheet mentions it because proper layout and snubber design aim to dampen this specific negative excursion, not just the overall ringing amplitude.

 

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