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Gain Margin on the Buck Converter

GARAM AN
Intellectual 1990 points

Hi all,

Phase margin and gain margin is important on the stability, the phase margin should be over than 45 degree for the stability.

I could find the gain margin is also over than 6~10dB, could you please explain the reason that the gain margin is also important on the stability?

Thank you

  • 0
    TI__Genius 14876 points

    Hello User,

    Gain margin is already defined by power architecture of the device and is not something you can influence using external components. Having a good gain before cut frequency will define the speed of your system.

    On the application side, we only focus on the phase margin which will define stability of your power supply and is the only parameter with either external compensation or feed-forward capacitor you can influence.

    Let me know if you have any other questions.

    Thank you,

    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 14876 points

    Hello user,

    Was I able to give you enough information? Do you have any further questions on this topic?
    Let me know.

    Thanks a lot!

    Regards,

    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Intellectual 1990 points

    Thank you Dorian,

    I could not catch that you mentioned "Gain margin is already defined by power architecture of the device"

    Could you please explain more detail?

    I could find that the gain margin changes depending on the inductor on the buck or boost converter.

  • 0 in reply to GARAM AN
    TI__Genius 14876 points

    Hello,

    Power-MOSFETs, Output filter with Inductor and output capacitor bank defines your open loop Gain.

    Depending on device specification this might differ from device to device, and also related to control topology : current/voltage/DCS mode.

    Changing your inductor value will modify the current variation in your inductor and then challenge the control loop which was defined for certain range of current variation. 

    You can have some flexibility in inductor selection but will then depends on device specification, and if control topology of this device can allow this change without making the system unstable.

    Thanks,

    Dorian