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Switcherpro buried

Olli Mannisto
Expert 1750 points
Other Parts Discussed in Thread: TPS5401

I want to create a design using the TPS5401. Nothing special here, just 35v to 3.3V 0.5A SMPS. And before someone chimes in, real load is more like 200mA. 

Now the website crams webench down your throat sideways. Back in the day you could find Switcherpro as an alternative at least if you dug a little bit. Now it seems that it's not possible to find it unless you know what it's called. Why use switcherpro? Well, it has to my mind much better feedback loop calculator. If for no other reason that it tells you where the poles and zeros are. Webench simplifies this out so as not to make designers scared. 

And of course, TPS5401 is not supported properly by Webench so you're out of luck if you were planning on using non-optimal parts used elsewhere in your design. At least wrt tuning the feedback loop. 

So is the Switcherpro now persona non grata? Unless you come to the forum and can see people referring to it?

  • 0
    TI__Guru**** 191445 points

    Yes switcherpro is pretty much legacy software now.  It has not had any updates in a few years now, and will not have any in the future.  I also still use it occasionally.  I have requested many times that webench include some of the functionality that is in switcherpro.  Maybe someday, we'll see.

  • 0 in reply to JohnTucker
    Expert 1750 points
    Yup, I thought as much.

    Still it'd be nice if you had a link at least SOMEWHERE in the power management page. Switcherpro is very convenient for calculating those poles and zeros and it shows the result in a nice graphical view. Now of course the results can be a bit informative but never the less.

    WRT Webench, does it take the CMC into account? There's a paper by mr Sheehan (SNVA555) which tells us in great detail the usual method of simple ignoring the current feedback loop is simply wrong. Of course to allow for CMC you have to know some parameters about the insides of the controller not many vendors give such as the actual Vpp of the current feedback comparator input.
  • 0 in reply to Olli Mannisto
    TI__Guru**** 191445 points

    let me see if I can get a switcherpro link added.

    as to your other question, do you mean CMC = current mode control?

  • 0 in reply to JohnTucker
    Expert 1750 points

    Yes, Current Mode Control. 

    It's non-trivial to model the feedback loop of a CMC controller properly as that white paper among others explains.

  • 0 in reply to Olli Mannisto
    TI__Guru**** 191445 points

    For current mode control, the feedback portion is straight forward.  The trick is the power stage with slope compensation.  For ideal current mode with no slope compensation, the power stage is simply gain and a simple pole at 1/2*pi*Ro*Co as the inductor is an ideal current source. as slope compensation is introduce, it does become complicated.  so far as I know, webench models this correctly, but it is difficult to tell as webench does not show the power stage gain and phase characteristic.