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WEBENCH® Tools/LM5155: 350W+ Output

Part Number: LM5155
Other Parts Discussed in Thread: , LM5122, TPS40210

Tool/software: WEBENCH® Design Tools


I plan to use the lm5155 for one of our product that needs to meet the following requirements:

-Vin: 20-32VDC

-Vout: 110VDC @ 3.2A

When using Webench I got this schematic:

I also ordered the LM5155EVM-BST eval board and modded it according to the webench design above. The IC temperature got to 60 degree C when supplying 0.2A. At 0.7A it stops switching and the the Power MOS that I use (IXFB150N65X2 + Heatsink) gets very hot (80-90 degree C) and keeps getting hotter.

Is there a strategy that I can use to reduce the heat?

Is this design even suitable for my needs? If not what other design can I use?

Thanks in advance,


  • Hi Sylvain,

    Thank you for using the LM5155.  I am afraid this driver is not strong enough to drive the FET to process 350W.  You may employ an external driver to enhance the driving capability, or reduce the switching frequency to reduce the switching losses. 

    If you don't want to use additional driver, you can consider the LM5122, and just use the LO but leave HO, SW and HB grounded, then you should be able to operate more efficiently:  the LM5122 has 3A driver.


    Youhao Xi, Applications Engineering

  • Hi Youhao,

    Thank you for your support. Do you have an example with an external driver?

    Also, why the lm5122 didn't show up on webench for this application?



  • Hi Sylvain,

    I don't have a drawing of LM5155 with external driver, but you can refer to the following TPS40210 ref design which uses external driver consisting of two bipolar.

    In Webench, the LM5122 is designated for design with synchronous rectifier, and the output voltage is limited to 100V.  In your case you don't have to use the sync FET function but a diode rectifier should work.