Hi team
Please have a look on question below from the designer:
"just a question regarding the ripple limits and this, just to clarify something we saw during the analysis…
Look this image:
These are the values between 275KHz and 550KHz of the TPS65400 running MRR precompiled binary we can find in the installation directory.
In that picture I have also represented the limit (the line) specified in the datasheet as maximum ripple. As the value was only available at 275KHz and 550KHz I did a linear interpolation between those values, and I got that line. And then, I also added the “average of noise” (dotted line) for all the period considering the last 255 values. (This range has more than 56.000 points, so 255 points is not so much).
Plotting all this data together, I see different things. The first is that there are a lot of spikes that goes over the limits specified, but they are not “constant”, just spur of a few freqs with a very high value. The other is that the average use to be below the limit in all the range, except at 500KHz where the switching freq of the PMIC was set.
My point here is, will be enough make the average value go below the limit? Or should be all the spikes bellow the limit for all the range?
With the tests done so far, we’ve identified that it’s quite hard to keep all the spikes below the limit in all the range specified, as the switching frequency of the PMIC, for example, has a great impact and goes above the limit and maybe that “noise average” represents in a better way the overall noise that has our supply rails.
What do you think?
"
Rgds, Jose
