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PI Analysis!

JohnsonMiller , 06-10-2021, 02:48 AM
Do we really need PI analysis?

I had a discussion with a friend of mine regarding SI/PI, do agree that SI is essential, but what about PI? In our design, we usually deploy many plane layers, and importantly, completely obey chip manufacturer rules on powering, also add an overdesign. Do we still need to invest in PI?

In my opinion, PI is almost like an auto-router, it exists but nobody uses it; it is just for marketing. I would like to see what you think?
Lakshmi , 06-10-2021, 03:02 AM
Yes, of course, PI is also very important. in very dense board design and high speed.
Because if you consider the core voltage of DDR/SOC, they will have very tight tolerance You must make sure they are within that tolerance else they will not be on.
By doing analysis you can see the IR drop visually as well as the current density accordingly you can change or continue on the layout side.
Reference: https://www.youtube.com/watch?v=w-j9sGzJZYs
qdrives , 06-10-2021, 01:56 PM
For most low speed, high voltage (3.3V & 5V) and low current (< 100mA) it will not be needed.
There are two designs I worked with where PI comes to mind:
1) The first design was a 400MHz STM32H7 system (not my design). That system had a bad layout. There were some unexplained issues too, but it was not clear if this was caused by: bugs in the MCU itself, the combination of peripherals, bad gnd plane and connection to it (including decoupling caps), inductance in the (power) traces, no SI (EMC noise), etc. It used an older type MCU and the newer one had an improved power regulator which made it able to run at even 480MHz.
2) A motor controller where a slight difference was measured between positive and negative current. I used a PDN evaluation in Altium to 'measure' the difference in resistance in the Gnd planes from the two points back to the source. It matched what I empirically measured.
qdrives , 06-11-2021, 06:26 AM
A more interesting video is this one: https://www.youtube.com/watch?v=wbYzPwuEHPw
robertferanec , 06-14-2021, 07:51 AM
It may depend on what kind of boards you design. I would say higher the currents, more interesting the software can be for you.

It is definitely very nice to play with the software and if it is part of a package e.g. if you buy SI you get PI for free, definitely go for it. Would I buy it for my own company for the kind of boards I design? No, I would not buy it - simply, because the boards I design it is possible to design without the software. That is for example the reason why I have not bought Altium's PDN Analyzer.

Could the simulations help you to improve your boards? Yes, however, do you have time, people and money for it? Would you like to invest money and time into simulations even if your boards are working perfectly fine without them (even they are not ideal)? So, it is not only about the software itself, there are more factors what need to be considered.
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