• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 4 answers
  • Subscribers 62 subscribers
  • Views 274 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM3150: WEBENCH simulation result question

David Huang
Intellectual 2285 points
Part Number: LM3150
Other Parts Discussed in Thread: LM61460, LM76005, , LM5145

Hi Team

My customer is using the WEBENCH for load transient simulation, and is having some questions regarding the result.

1.  Why is the Vout 15V while the plot is at 15.6V?

2. Why is the overshot voltage not dropping back?

For detailed information and simulation setup, please check the image & PDF below.

Thanks

David

  • 0
    TI__Guru* 76102 points

    Hi David,

    Send on the schematic if possible. If there is large ripple amplitude at FB, it may increase the DC output voltage (as the valley of the ripple is regulated in a COT-based controller).

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Intellectual 2285 points

    Hi Tim

    I think the PDF file I upload disappeared for some reason...

    Below you can find a screenshot for the schematic of the setup.

    Regards

    David

  • 0 in reply to David Huang
    TI__Guru* 76102 points

    Thanks, David.

    The AC voltage coupled to FB is effectively sinusoidal based on the ceramic output cap (the internal ripple injection waveform needs to overcome this to maintain stability).

    If this is a 25V to 15V/4A application, my recommendation is to use a converter (with integrated FETs), such as the LM61460 or LM76005 converter families. This provides an easy-to-use optimal solution with small size and low cost.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Intellectual 2285 points

    Hi Tim

    Thanks for the recommendations.

    For LM3150 though I still have doubts regarding the first 2 questions I post.

    You mentioned about ripple at FB may cause the output to be 15.6V even though the setting is 15V, is this to be expected in actual use as well & how large is the ripple? Also, does that mean an LDO is required for a precise output if using LM3150?

    And why does the overshot voltage not dropping back?

    Looking forward to your response.

    Regards

    David

  • 0 in reply to David Huang
    TI__Guru* 76102 points

    Hi David,

    Please send the voltge waveform at FB. If there is substantial ripple, then the output voltage at no load will run higher as the COT controller regulates at the valley of the ripple at FB.

    If you need accurate regulation, please consider the LM5145 controller or the LM61460 converter.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    TI__Intellectual 2285 points

    Hi Tim

    Thanks for the response.

    You mentioned that the output voltage will run higher at no load if there's ripple, but the simulation should have included load already and the output was still higher than the setting.

    Also if the ripple at the FB is the problem, does adding higher inductance do anything good to this issue?

    The customer was pulling 4A and have set the ΔIL=1.26A(30% of the output). Do we have a recommended ripple rating that prevents this problem?

    Regards

    David

  • 0 in reply to David Huang
    TI__Guru* 76102 points

    Hi David,

    Try adding more output cap as the 22uF will derate substantially at 15Vout. Also, consider removing the FF cap as there's no benefit to coupling sinusoidal ripple from the output ceramic into FB (this basically sets unity gain from VOUT to FB).

    Have you tried this configuration using a modified EVM?

    Regards,

    Tim