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Thermal simulation problem

Olli Mannisto
Expert 1750 points
Other Parts Discussed in Thread: LM5022

I have a 24-to-55V 4.5A design with LM5022 controller. There is a problem as the design requires using two FETs and apparently the thermal simulator does not like this. As far as I can tell the mosfet is "floating" and heats up to a comfy 1156 degrees celcius. I can move one of the two FETs in the thermal simulator configuration but cannot interact with the other. By default both are on top of each other in a copper cut-out. 

Any way TI guys could take a look at that? Also it'd be double plus good if some power mosfets I asked for earlier would be implemented. There are still only two available for this kind of spec.. 

  • 0
    TI__Mastermind 41310 points

    Olli,

    I will forward this to the thermal team. I did confirm what you were seeing. Thanks for your patience while we investigate the issue.

  • 0
    TI__Prodigy 240 points

    Olli,

    I took a look at your design.  You are correct about the Parallel FETs.  WebTHERM(TM) is not able to handle their placement properly.  Also your design has a custom inductor which is also not supported in WebTHERM (all heat focused at a pin point).   Hence the inferno that you see in your results.

    The Peak SW current is over 12.5A, which caused these non-standard circuit solution to show up in your design.

    The Webench product owner will be taking a look at the design support for the LM5022.

    Regards,
    Richard Levin
    Webench Physical Realm Tools Manager

  • 0 in reply to Richard Levin
    Expert 1750 points
    The inductor should be actually a stock part? Vishay Dale IHLP6767GZER8R2M01?

    The only custom part I have is the output ceramic capacitor. I'm not sure if webench takes DC bias into account or not and the DC bias effect is dominant at 50V output voltage so I made a custom capacitor with the actual effective capacitance. Having a larger selection of high power FETs would be nice too.

    Yes, the design is moderately high power (200W peak). I have our mechanical engineers working on thermal simulation(s) as well but the webench simulator would be a nice thing to play around with..