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I am doing Modelling of Buck Converter for LT3890 (Datasheet link attached) for Frequency response analysis . I have some reference model of Buck converter ,please refer below image enter image description here

Datasheet Link: https://www.analog.com/media/en/technical-documentation/data-sheets/LTC3890.pdf

Now I can find G1 value from datasheet and it is mentioned 2mOhm for 1.2V enter image description here

Now My Converter is 5V output and max output load is 4A so how can I decide Gm value for G2? Let's say if I get the G2 value for maximum load ,Do I need to change for Min load Frequency response Analysis ?

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  • \$\begingroup\$ I don't understand, why don't you use an averaged model for this exercise? There are plenty to choose from and you it's a no brainer to implement. Where is the inductor in your circuit? \$\endgroup\$
    – Verbal Kint
    Commented Feb 27 at 10:40
  • \$\begingroup\$ Hi Sir as this is current mode control so inductor is ignored (reference :electronicdesign.com/technologies/power/article/21281998/…) ....In Ltspice we dont have generic block of transconductance amplifier like in simplis ...thats why it is replaced with voltage controlled current source ....Could you please suggest any average model for LTspice \$\endgroup\$
    – Power Path
    Commented Feb 27 at 10:49
  • \$\begingroup\$ Idea of this model is taken from Sam Ben Yakov Video youtube.com/watch?v=dyLzh6gzisA \$\endgroup\$
    – Power Path
    Commented Feb 27 at 10:56
  • \$\begingroup\$ A current-mode-controlled buck is a 3rd-order system: a low-frequency pole and two sub-harmonic poles located at half \$F_{sw}\$. You need to predict these sub-harmonic oscillations to damp them properly with slope compensation, what your simple model cannot do. \$\endgroup\$
    – Verbal Kint
    Commented Feb 27 at 11:05
  • \$\begingroup\$ Hi Sir Many Thanks! Could you please share some link of any reference model and theory behind the concept of 3rd order so I will try to model accordingly ...I am new to the power converter so I dont have in-depth understanding .I searched over internet regarding model which can predict sub-harmonic oscillation but everywhere I am seeing current model buck converter approximated as 1st order so unable proceed further ..once again Thanks for your response \$\endgroup\$
    – Power Path
    Commented Feb 27 at 11:16

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The easiest and fastest way to obtain the ac response of a switching cell such as a buck in current-mode, is to use a dedicated averaged model. I use the PWM switch model introduced by Vatché Vorpérian in 1986 and available in auto-toggling versions DCM/CCM operated in VM or CM from different simulators. There are examples of this PWM switch ported in LTspice you can download in the bottom of my webpage:

enter image description here

You can check this document that wrote a while ago already and it describes some models for CM simulations. For more information on small-signal modeling, check my seminars list, particularly 5 and 6, all in free download. I also remember having dedicated an entire APEC seminar to the buck converter, seminar 11.

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  • \$\begingroup\$ Hi sir from last couple of days I have observed your website is not opening ...earlier it's used to opening but now it is showing" This site uses an untrusted SSL security certificate" message. \$\endgroup\$
    – Power Path
    Commented Feb 28 at 3:41
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    \$\begingroup\$ Hello Power Path, I have reported this to the guys hosting my site and asked them to see what they could do. Thank you for pointing this out to me. \$\endgroup\$
    – Verbal Kint
    Commented Feb 28 at 8:05
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    \$\begingroup\$ @PowerPath, the provider installed the certificate and it should be ok now if you access my page. Thank you! \$\endgroup\$
    – Verbal Kint
    Commented Feb 28 at 11:41
  • \$\begingroup\$ Yes sir ,I am able to access now ...Thanks! \$\endgroup\$
    – Power Path
    Commented Feb 28 at 12:48

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