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LM2611: Selecting Inductor Values

Ryan.Bishop
Expert 3900 points
Part Number: LM2611

Hi,

With the LM2611, slope compensation is added internally, and the datasheet says “use 10 to 22uH”.  Is this for the coupled or uncoupled inductors (customer will be using coupled)?  The inductor ripple current is pretty high for 12Vin, -15Vout, 200mA out – 100mA pk-pk for a 22uH coupled inductor.

Can any adjustments be made to accommodate higher inductor values?

Thanks!

Ryan B.

  • 0
    TI__Guru 74420 points
    The requirement should also apply to the coupled inductors. For higher inductance, you will just need to be careful to check the stability in the entire range of operation.
  • 0 in reply to Youhao Xi
    TI__Expert 3900 points
    Thank you Youhao,

    I think I still need clarification on this topic. I've been playing around with TI's Power Stage Designer tool, and I've confirmed that using 22uH coupled inductors results in the same amount of input/output current ripple as 44uH single inductors. This makes me think that the device won't "see" the same inductance if I used 22uH coupled vs 22uH singles.

    If I used 22uH coupled inductors, would I be exceeding the 10uH-22uH guidelines since it seems to behave like it has 44uH single inductors placed? Or is the vise-versa?

    I hope that made sense, let me know if you have any questions for me!

    Thank you,
    Ryan B.
  • 0 in reply to Youhao Xi
    TI__Expert 3900 points
    Hi Youhao,

    Is there any clarification you could offer on my previous post? I want to make sure the customer get's accurate information so they can design with this part.

    Regards,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Guru 74420 points
    Hi Ryan,

    Sorry this is overlooked. In the future you can always shoot me an email if you do not get a reply after a couple of days.

    The coupled inductors just have flux linkage between the two inductors but each will still be seen as its face value, namely 22uH in this case.

    Thanks,
    Youhao