• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 65 subscribers
  • Views 423 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.

Original question:

LM2596: Output cap: aluminium or tantalum at minus 40 C in WEBENCH

LM2596: choose "alternate part" out capacitor in WEBENCH

Vladimir Naumenkov
Prodigy 120 points
Part Number: LM2596

Dear Frank, Dear Carol, good morning

Please answer:

1) When I choose an alternate out capacitor in WEBENCH and I create a "custom part", then the capacitance value and ESR are enough to correctly determine the phase margin parameter?

2) What does this mean: - "derated Cap per Cap" ?   For example I use two capacitors of 100 microfarads each, then I must type "100" or "200"?  I think "100",  since I type quantity 2.

3) ESR per Cap - it is the ESR of one Cap (for example 50 mOhm). If I use two caps, then I must type "50" or "25"?  I think "50",  since I type quantity 2.

4) I made calculation, please see "WBdesignLM2596_1" and I want to create a custom out cap. I use two cap 100 microF, 150 mOhm and I see warning, please see "593D107X9020E2ETE3" file.

Then I click "SAVE" (100 microF,150 mOhm, two caps) and I get - please see "WBdesignLM2596_2".  I understand, that at first the program "does not see" the fact that I installed not one capacitor, but two. And then, when calculating, WEBENCH sees that are two capacitors?

QUESTION:  Can I assume that everything is fine? Or not? Phase margin  parameter in both cases is within the allowable range.

5) Please remind me what is the maximum allowable value of  the Phase margin  parameter?

TIA

Vladimir Naumenkov

WBDesign_LM2596__1.pdf

593D107X9020E2ETE3.docx

WBDesignLM2596_2.pdf

  • +1
    TI__Guru 73615 points

    Hello

    I will assign this to our Webench team.

    Thanks

  • +1 in reply to Frank De Stasi
    Prodigy 120 points

    Dear Frank, thank you

    Sincerely,

    Vladimir Naumenkov

  • +1
    TI__Prodigy 330 points

    Hey Vladimir,

    1: Yeah, the capacitance (after derating!) & ESR are enough for webench to model the capacitor & the system.

    2: Correct - it's the derated value of each capacitor. For instance if you're using a 22uF capacitor and it derates to 10uF at Vout = 5.2V, you'd put in 10uF. If you're using 2 capacitors in parallel at the output, you'd use the characteristics for 1 capacitor and put 2 in the quantity field. This is to model ESR with 2 capacitors accurately.

    3: Same as 2 - yeah, put in 50 and use 2 for the quantity.

    4: when you set the quantity to 2, webench knows that you intend to use 2 parallel, identical capacitors at the output (indicated by the 'Qty: 2' under the capacitor characteristics, and the 2 in the quantity column in the generated pdf). Whether the high ESR on the output capacitance is okay is dependent on the application - it increases ripple voltage & efficiency will drop a little.

    5: Your phase margin must be above 40 degrees or so, ideally closer/above 60 degrees. 70 degrees is fine. There isn't really a maximum value (although too high of a phase margin will make the converter slow), but there is a minimum. 

    Let us know if you have any other questions!

  • 0 in reply to Sekhar Musunuri
    Prodigy 120 points

    Dear Sekhar, thank you

    Sincerely,

    Vladimir Naumenkov