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WEBENCH® Tools/LM25085: About heat generation of LM25085

user1731820
Prodigy 30 points
Part Number: LM25085

Tool/software: WEBENCH® Design Tools

We are considering adopting your company's LM25085 for new projects.

We have used your company's WEBENCH under the conditions of Vin = 24V, Vout = Max18.1V, Typ10.5V, Iout = Max10A, Typ4.2A.

When run on Max, Rt = 698 kΩ, Frequency = 164.833 kHz, and IC Pd = 395.53 mW.

When executed with Typ, Rt = 105 kΩ, Frequency = 556.256 kHz, and IC Pd = 1.264 W mW.

Since the value of IC Pd is directly linked to the heat generation of the IC, the heat generation is 17.7 ° C for Max and 56.6 ° C for Typ, which is three times as much as the constant for Typ.

What is the reason for increasing the Frequency in WEBENCH at the time of Typ?

Also, I would like to suppress heat generation to about 20 ° C, but if I increase Rt, will it affect other constants such as L1 and Cff?

Is it possible to change the value of Rt and recalculate with WEBENCH?

  • 0
    TI__Mastermind 22299 points

    Hello,

    Are you planning to use two different output voltages in the same design, ie switching from 18.1V / 10A to 10.5V / 4A ?

    You can use a preferred switching frequency in the WEBENCH option to the left. It will recalculate the Cff, RT and L.

    Yes lower switching frequencies will lead to lower switching losses and IC power dissipation.

    However if the switching frequency is too low the load-transient response will be poor (You can also simulate load transient in WEBENCH)

    Higher switching frequency will have better response and have a smaller solution size.

    Hope this helps, let me know if you have further questions.

    -Orlando