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LM61460-Q1: LM61460 / LM61430 : internal RC of the error amplifier (compensation circuit)

Cyrille Schlencker
Prodigy 30 points

Part Number: LM61460-Q1
Other Parts Discussed in Thread: LM61460, LM61460EVM, LMR14020, , TINA-TI

Hello,

I work on a new Buck design to improve the overall efficiency of the power conversion.

In the LM61460 and LM61460EVM datasheet there is Rff and Cff in parallel with the Rfbt resistor of the feedback voltage divider which correspond to the type III compensator circuit.

After searching the web for additionnal informations I found this document SNVA798 which gives the components value for the RC used inside of the Buck converter IC for LMR14020QDPR.

www.ti.com/.../snva798.pdf

image.png

It is possible to get the same level of information for LM61460 / LM61430 Buck converter IC ?

The goal is to simulate the converter using SIMPLIS or other simulation tool which includes the compensator circuit to know the gain and phase margin.

  • 0
    TI__Genius 14410 points

    Thanks for your question. I will look into it and get back to you

    Thanks and Regards

    Naresh

  • 0 in reply to Naresh Adepu
    TI__Genius 14410 points

    Hello Cyrille

    For LM61460 / LM61430 the internal error‑amplifier and compensation network values (the RC shown in SNVA798 for LMR14020) are not published and are not available as a separate model, so the same level of detail cannot be provided. For loop‑stability work the recommended approach is to use the datasheet’s external compensation design guidelines and either: 1) simulate with TI’s released LM6146x average/PSPICE models, which already include the internal network, or 2) measure Bode plots on hardware following the evaluation‑module documentation.

    Thanks and Regards

    Naresh

  • 0 in reply to Naresh Adepu
    Prodigy 30 points

    Yes this is what I understood Naresh by looking at the LM61460 datasheet.

    In my Buck design I want to use the converter to generate 3V3 (value given in the LM61460 datasheet) and 1V2 (no info given in the LM61460 datasheet) for Cff and Rff values.

    I don't have access to a VNA / FRA to do the Bode plot using the injection resistor placed on the demo board for LM61460.

    The oscilloscope I'm using RTB2004 only have a Bode plotting feature but we don't have a Wideband Injection Transformer available in the lab.

    Also the model I downloaded for LM61460 doesn't run in transient analysis for an output voltage of 1V2 (lower resistor of the feedback voltage divider to 500k). I downloaded the file snvmbx5a.TSC to use with TINA-TI from the LM61460-Q1 page.

  • 0 in reply to Cyrille Schlencker
    TI__Genius 14410 points

    Thanks for  your question

    we will look into it and get back to you

  • 0 in reply to Naresh Adepu
    TI__Genius 14410 points

    Thanks Cyrille, that understanding is correct. For LM61460 the internal error‑amp and compensation values are not provided separately, so the recommended method is still to design using the datasheet external‑network guidelines and the released average/PSPICE models, and then verify stability by Bode measurement when you have access to suitable equipment.


    For now, you can:
    • Use the 3.3 V reference design in the datasheet as a starting point for your 3.3 V and 1.2 V rails, keeping L and Cout within the ranges given in Table 9‑1 so they stay inside the guaranteed stability window.
    • Simulate both 3.3 V and 1.2 V cases with the LM61460 average model in TINA‑TI/PSPICE to check gain/phase margins; this does not require a VNA.
    • When lab access allows, you can follow the LM61460‑Q1 EVM user guide, which shows the injection‑resistor and Vinj test node for Bode plots, and replicate that arrangement on your hardware.
    Because TI does not publish the internal comp network, there is unfortunately no additional numerical data to share beyond these models and guidelines, so as long as your L/C values follow the datasheet table and simulation shows adequate phase margin, the design is considered compliant.

    Hope this helps. I am closing this thread.

    Thanks and Regards

    Naresh