SparkFun Forums

[ircident]

Hi, I'm trying to build a board with the FT232RL chip on it. I don't have any of the smd inductors specified in the data sheet. I found a through hole bead I may be able to use instead. Can anyone say whether the this one below would serve the same purpose?



Thank you for the help.

[Philba]

yeah, just by looking at a picture with no part number or spec sheet I can tell you unequivocally - maybe.

[ircident]

I was thinking as much. I think I may have just lucked out. Found a bunch of smd ferrites sitting on an old motherboard's usb and firewire ports. Using those are probably a better bet.

[henryhallam]

Don't tell anyone - but you can just use a wire and it'll work fine

[Philba]

I actually wondered about the issue - I believe it's to suppress interference. However, some reference designs use one and some don't. I've never seen a clear explanation why FTDI specs one and microchip doesn't.

[Fake_Name]

That is (almost definitely) indeed a ferrite bead. if the black section moves freely on the wire, then it definitely is.

The point of the ferrite is to block some of the noise coming from the PC on the v5.0 line of the USB connection from getting into the 232 and and any devices run off the v5.0 rail.

Small ferrites really only work in the few hundred Mhz and up range, and the actual ammount of noise produced by a PC varies.

Basically, it's a precaution.

Wikipedia has a article on ferrite beads (with some good links):
http://en.wikipedia.org/wiki/Ferrite_bead

[Twingy]

I've used this chip extensively and I use the circuit example on the data sheet that does _not_ required the bead and they work on all of my computers and all of my serial devices.