I bumped into a couple of strange symbols that look like inductors or ferrite beads, I'm not sure what this is. Does anyone know what it is and what is the purpose of it? My guess is it has something to do with a general use of USB as a power supply. There are no parameters or anything to go by: enter image description here

Here is a link to the document that has this schematic on page 28: https://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT4232H.pdf

My plan is to ignore it, but I am afraid it might be important for the stability of this chip

EDIT: it seems to be an LC filter, as mentioned on page 9 of the datasheet. I'm still not sure if that is what it is or how to make it.


1 Answer 1


My plan is to ignore it, but I am afraid it might be important for the stability of this chip

Ignore at your peril: -

enter image description here

If you google around for USB interface circuits that use this chip, you'll find the appropriate device to use for the inductor. I've build one myself (and did the same) but, for the life of me I just cannot remember what I fitted other than that I went on the hunt for what other people had used and got an answer.

It's a bit crap that the data sheet isn't more forthcoming on this part of course. OK, here's a start: -

enter image description here

Located in this document. They are 600 ohm ferrite beads. I expect if you dig a bit more you'll find the part number. Use them.

You can find the part number in this document. It's an 0603 size ferrite bead so not hard to fit and, there is never a good reason to ignore them.

  • \$\begingroup\$ I agree with Andyaka. For a one-off hobby project for your personal use, it will be fine to ignore, but it may end up with less reliable device. If making a mass-market product that has to pass EMC tests, you would not ignore it, it is so simple to make. \$\endgroup\$
    – Justme
    May 3, 2020 at 7:46
  • 1
    \$\begingroup\$ Just fit them and no argument whether it's a one-off or not. \$\endgroup\$
    – Andy aka
    May 3, 2020 at 7:49

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