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LM5170: LM5170 inner current loop

Siddheswar Sen
Prodigy 160 points
Part Number: LM5170

Please refer equation no. 24 of LM5170 datasheet. I am trying to understand the small signal model that has been represented by the equation. I have also seen the related lecture of Garrett Roecker "training.ti.com/average-current-mode-control-bidirectional-dcdc-systems" and the document "https://training.ti.com/sites/default/files/docs/Average_Current_Mode_Control_of_Bi_Directional_DCDC_Systems.pdf " 

However, I am unable to derive the equation 24 of the datasheet.

Can anyone please help me to understand and derive the equation.

Regards,

Siddheswar Sen

  • 0
    TI__Guru 58225 points

    Hello Siddheswar,

    The expert for this device and model is not in the office at the moment. I am sorry, but it will take until next week to get an answer for your question.

  • 0
    TI__Mastermind 21720 points

    Hi Siddheswar,

    Equation 24 is a simplification of the inner control loop that assumes that there is no ripple on the output voltage. This helps to simplify the equation down for hand calculations. For systems with a battery on the input and a battery on the output this is a accurate equations. This is due to the batteries having a large capacitance which resists voltage changes.

    In the training the impedance is considered for systems that might have a smaller output capacitance or for engineers that want a more in-depth understanding of the control loop equations. This is a more generic approach to modeling average current mode control.

    I hope that helps explain the equation in the datasheet. Please let me know if you have any questions.

    Thanks,

    Garrett