• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 65 subscribers
  • Views 853 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

WEBENCH® Tools/LM5022-Q1: what is the optimal slope compensation for boost DC/DC with duty cycle larger than 50%

Chris Zhao1
Expert 1240 points
Part Number: LM5022-Q1

Tool/software: WEBENCH® Design Tools

Hi experts,

I came to this forum for help again. I'm designing a boost circuit with LM5022-Q1, 12V+-5% input, 54V/2.4A output.

I copied part of page12 of datasheet below, it says the optimal compensation is proportional to inductor current during MOSFET off;

In page21, there is a formula to calculate the Rsns, from it I can find the ratio to plus (Vo -VI)/L is 3D/fsw = 3DT, is that right?

If so, why does this value is used here, can I use just 1, or 1/2, or other value?

Thanks

Chris

  • 0
    TI__Guru* 75895 points
    The formula a simplified and conservative way to calculation to select the Rsns with adequate slope compensation. Ideally 3 can be reduced to 2, but it does not leave any margin to cover the inductor tolerance.
  • 0 in reply to Youhao Xi
    Expert 1240 points

    Hi Youhao,

    Thanks for your explanation, I'm still confused.

    In page21, there are two equations, which are used to calculate Rsns and Rs2, VCL is used in both,

    equation (41) is kind of easy to understand, as it's shown in Figure 13.;

    while for equation (36), what's the meaning of it, based on what kind of theory to get this equation?

    Thanks

    Chris

  • 0 in reply to Chris Zhao1
    TI__Mastermind 21720 points

    The current limit equation can be derived as shown below. This is true regardless of the topology. To simplify the equation the Vslope term can be removed.

    For a current mode control architecture the optimal slope compensation should be equivalent to the down slope of the inductor times the current sense gain. It is okay to have more slope compensation than a factor of 1. For a boost converter this is:

    Which yields

    In the datasheet K=(3*D/fsw), which is there to give margin and help fit a majority of the applications while keeping the equation fairly simple. Back solving for Rsense is how the equation in the datasheet is derived.

    Equation 40 is then used to make the slope compensation match the above K factor that was used.

    Please let me know if you have any questions.

    Thanks,

    Garrett Roecker