4 Replies Latest reply on Dec 3, 2017 9:16 PM by mjk

    Advanced Decoupling Analysis with VRM

    mjk

      Hi, expert.

       

      I have a question about advance decoupling analysis.

       

      I found out that there is VRM effect in Lumped Decoupling Analysis.

       

      vrm1.png

       

      However, for Advanced Decoupling Analysis I couldn’t find any VRM effect in the results.

      I’d like to know if there are any mistakes in my settings.

      I did a test with a reference design. : BeagleBone Black - Mentor Graphics

       

      vrm2.png

      vrm3.png

       

      Thank you.

        • 1. Re: Advanced Decoupling Analysis with VRM
          weston_beal

          MJK,

           

          I don't have that design to see if there is something odd in the PDN layout. Your setup looks correct from the pictures you provided, but maybe the effect of the VRM is just hidden. Try reducing the inductance of the VRM model and reducing the capacitance values in the capacitor models. This will increase the resonant frequencies and hopefully bring into view the effect of the VRM at the low end of the frequency scan.

           

          Because Advanced Decoupling Analysis models the whole PDN with its distributed inductance effect, the impedance between the power pins (measurement points) and the VRM might be large enough to mask the effect of the VRM. Maybe reducing the inductance of the VRM model to something absurdly low will bring down the impedance to the point that you can observe it.

           

          Regards,

          Weston

          • 2. Re: Advanced Decoupling Analysis with VRM
            mjk

            Dear Wetson,

             

            Thank you for answering my question.

             

            As your advice, I set the inductance of VRM to 0.1uH, 0.01uH and even 0uH

             

            and I did advanced decoupling analysis with small capacitances such as 10pF.

             

            But I couldn't see VRM effect.

             

            이미지 9.png

             

            Is still VRM effect hidden?

             

            Is there anything I miss?

             

             

            Thank you.

            • 3. Re: Advanced Decoupling Analysis with VRM
              weston_beal

              MJK,

               

              I worked on this a bit, too, and I found the same result. I think that the correct method to apply a VRM model for Advanced Decoupling Analysis is by defining a pin group on the VRM component. I went through that method but still did not get expected results. I suggest that you create an SR on Support Center so that the support team can research this issue in detail. It might be a defect that needs to be recorded.

               

              Regards,

              Weston

              • 4. Re: Advanced Decoupling Analysis with VRM
                mjk

                Dear Wetson,

                 

                Thank you for checking this problems.

                 

                I'll create an SR as you suggest,

                 

                Thank you.