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LM25180: WEBENCH doesn't run

Kuramochi Tadahiko
Guru 28715 points
Part Number: LM25180
Other Parts Discussed in Thread: LM5180,

Hi,

WEBENCH doesn't run on the following condition;

However, it does run on the LM5180 page.

I think that LM25180 is the same as LM5180 except for input voltage tolerance.

Which results are correct? 

Best Regards,

Kuramochi

  • 0
    Genius 4910 points

    Hello Kuramochi-san

    Please note that for the above input/output conditions, the design fails to create as the calculated switch node voltage exceeds the maximum limit of 65V (eqn 20 in datasheet). Designs can be created for LM5180 device as it has 100V as maximum limit voltage  at switch node.

    Let me know if you need anything.

    Thanks and Regards,

    Atul

  • 0 in reply to Atul_Kulkarni
    Guru 28715 points

    Hi Atul-san,

    Thank you for your reply.

    I think that the maximum Vsw is calculated by VIN(max)+(VOUT+VD)*NPS.

    If NPS=1, the maximum Vsw does not exceed 65V on the above condition, because it is 38.4V.

    I checked this condition on the attached calculator.

    LM25180 PSR Flyback Converter Quickstart Tool.xlsx

    Do you think that this condition is not appropriate for LM25180?

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    Genius 4910 points

    Hello Kuramochi-san,

    You are correct, if NPS is 1 the then Vsw does not cross the 65V and IC can be used for this inputs. Kindly note that Webench has a bit complex algorithm which selects the transformer and includes multiple variables (Inductance value, number of turns, AWG Layer, strands, transformer losses which meets efficiency standards to name a few). For your input condition, Webench calculates the NPS as 2.85 and hence fails the design for Vsw voltage check (calculation below). Currently it’s not possible to change the NPS value dynamically in Webench (as we did in excel calculator) and will not be able to give you the design as well.

     

    Vclamp = 1.5 * Vout * Nps= 1.5*12*2.85 = 51.3 V

    Vsw = Vclamp + VinMax = 77.7 V (>65)

     

    We suggest two alternate solutions for this,

    1. Going ahead with LM5180 which is able to create the design for given input condition. And use this design as a starting point.

    2. Second solution would be sticking to LM25180 with lower NPS (Assuming NPS = 1, Dmax will be restricted to approx. 37 % eqn 14). But in this case, Webench design won't be available. We will have to use excel calculator instead of Webench to generate the external component values.

    Hope this clarifies.

    Thanks and Regards,

    Atul