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Switcher Pro result is different with my calculation

Stone Lee
Intellectual 310 points
Other Parts Discussed in Thread: TPS40211, TPS40210

Hi, gentleman :

I try to use Switcher PRO to design my project. But I found the result of SwitcherPro is different to my calculation according to TPS40211's datasheet. For Example :

1. The output capacitance is 56uF, but the result of Switcher PRO is 470uF.

2. The power inductor L1 is 8.2uH, but the result of Switcher PRO is 1uH

I recognize the switching frequency is different with my case, but I believe these parameters don't have so large difference. Can you give me some tips ?

BR

Stone

  • 0
    TI__Intellectual 1280 points

    Hello Stone,

    We have a TPS40210 model in SwitcherPro but no TPS40211, so I'm assuming that you're using that model.  The data sheet for this part is going to give some design hints and equations but the SwitcherPro tool is going to do a bit more to make sure you have an optimized design.   For example, in this case it's going to pick a 1uH inductor to put your design right on the edge of continous/discontious conduction mode.  This is ideal for this device because it reduces the effects of a Right Half Plane Zero which will be part of this design.   The Ouptut cap selection is really complicated in Switcherpro.  It is not exactly optimized for this device, so you might try selecting a smaller cap to see if SwitcherPro will warn you about any problems.  This part also had some output cap selection bugs recently fixed, but won't be available to you until 7/31 when we release the next version.  Switching Frequency will affect a lot of stuff.  So be careful there.  In general the higher the frequency the smaller value inductor you can use.

    Thanks

    heath