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Design >> Analog Design >> How to reduce the overshoot due to a RCL step response?
https://designers-guide.org/forum/YaBB.pl?num=1496311714

Message started by Jacki on Jun 1^st, 2017, 3:08am

Title: How to reduce the overshoot due to a RCL step response?
Post by Jacki on Jun 1^st, 2017, 3:08am

Hello,

I am facing a problem of overshoot ringing. I use 2.5 V IO transistors as the output stage, because of the parasitic inductors (estimated as 1 nH) at both VDD and VSS, the output signal starts overshoot and ringing a bit. This overshoot voltage (peak value is 3.8 V) is over the breakdowm voltage, I am afraid it will damage the transistor or reduce the life time. Does anybody have the experience on solving this overshoot problem?
I know the overshoot in the step response of the RCL is fundamental problem (as shown here http://www.cvel.clemson.edu/emc/calculators/RLC_Calculator/index.html), I try to reduce it, or else I have to change the transistors to 3.3 V IO transistors (bad option).
Any comments are highly appreciated.
Thank you.

Title: Re: How to reduce the overshoot due to a RCL step response?
Post by deba on Jun 1^st, 2017, 3:19am

You can size the damping resistor such that there is no overshoot. Q≤0.5 should do the job.

Title: Re: How to reduce the overshoot due to a RCL step response?
Post by Jacki on Jun 1^st, 2017, 4:04am

deba wrote on Jun 1^st, 2017, 3:19am:

You can size the damping resistor such that there is no overshoot. Q≤0.5 should do the job.

Thank you for your reply. I forget to mention that I cannot add the resistor to lower the Q, it also lowers the efficiency.

Title: Re: How to reduce the overshoot due to a RCL step response?
Post by Jacki on Jun 1^st, 2017, 4:14am

Also on-chip decoupling capacitor is not a choice because I don't have enough space for it, and off-chip decoupling capacitor between VDD and VSS doesn't help.

Title: Re: How to reduce the overshoot due to a RCL step response?
Post by Ken Kundert on Jun 1^st, 2017, 10:57am

You might try looking through Power Supply Noise Reduction and see if you find anything that helps.

-Ken

Title: Re: How to reduce the overshoot due to a RCL step response?
Post by Jacki on Jun 2^nd, 2017, 2:40am

Thank you very much Ken, I will try to see if the mutual inductance can help, also with the careful routing in the layout.