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LM5025: How can LM5025 be configured to drive high side N-FET Active clamp ?

Anindya Dasgupta61
Prodigy 60 points
Part Number: LM5025
Other Parts Discussed in Thread: , TL431

Hi,

We are trying to use LM5025 as a pwm controller to configure the dead times and drive the main and aux switch of a high side active clamp forward converter.   While it is implied from datasheet of LM5025A (SNVS293F - Revised Aug 2016 - page 3) that it can be used for a high-side N-channel switch but we are unable to understand how to do so since there is no example or application circuit for the same.  We shall be thankful to get help on this.

As for our application: the input voltage can vary from 26 V to 42V. For compensation, voltage mode control is being used with loop compensation realized by using TL431 in secondary side along with a optocoupler.

Thanks,

Anindya Dasgupta

 

  • 0
    TI__Mastermind 34465 points

    Hello Anindya,

    Most application of the active clamp use a low side p channel reset FET probably because it is so much easier to drive this part.

    However there are advantages in using an n channel FET in certain applications.
    Application note SLUA322 describes the design considerations in using a high side reset FET.

    The LM5025 can be configured for an n channel reset by an RSET resistor connected between TIME and REF.
    This produces out-of-phase OUT_A and OUT_B pulses with dead time.

    There are several versions of the LM5025 and I am attaching a document that highlights the differences between all these parts

    LM5025A Vs LM5027A Vs UCC2897A.pptx

    So far I have not been able to locate a reference design with a high side reset.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 60 points

    Hello John,

    Thanks for your email. I understand it is not going to be easy with high-side clamp and thus have re-done the analysis with low side clamp and P-FET to use LM5025. I would like to know more about the following regarding 5025:

    (i) How to set up Vcc ? Our supply varies from 26V to 42V and we want a gate pulse between 11V and 15V.  I prefer not want to be dependent on any auxiliary winding neither on linear regulator as efficiency for us is premium.

    (ii) Would also like to know more about the drive circuit of 5025 so that I can use a gate resistor of appropriate value.

    Thanks,

    Anindya