Objective Development Forums

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-06-18T08:21:04+02:00

For a low-speed USB device are the values of ther sries resistors at D+ and D- not very important. Values from (0)47 Ohm to 330(1000) Ohm are working.

Statistics: Posted by Guest — Wed Jun 18, 2008 8:21 am

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-05-21T04:32:12+02:00

tested, works fine.

Statistics: Posted by Guest — Wed May 21, 2008 4:32 am

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-05-20T19:34:45+02:00

Should work as well.

Statistics: Posted by christian — Tue May 20, 2008 7:34 pm

82 ohm?

2008-05-20T15:19:04+02:00

For some reason I ordered 82 ohm resistors instead of 68 ohm. I can't figure out why I thought it was 82, since every schematic I've checked says 68.

I'm guessing it shouldn't make a difference?

Statistics: Posted by Guest — Tue May 20, 2008 3:19 pm

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-04-24T18:07:51+02:00

Now everything's clear. Thank you.

Statistics: Posted by luke — Thu Apr 24, 2008 6:07 pm

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-04-23T16:42:58+02:00

These resistors have several functions:

* Limit the current if zener diodes are used for voltage limiting on D+ and D-.
* Limit the current in case of short circuit or if higher voltage is applied from extern.
* To some degree impedance matching to the cable when sending data.
* Low pass filter to avoid ringing when level is switched.

Having that said: You may omit these resistors if you have no cable and don't use zener diodes.

Statistics: Posted by christian — Wed Apr 23, 2008 4:42 pm

What's the purpose of 68ohm resistors on D+ and D- lines?

2008-04-22T12:15:31+02:00

Hi.

I couldn't find any information about them on the web. I bet they are needed since I've seen them in every single project using USB. I'd like to understand everything before I start soldering and it's the only mysterious part of the schematic.

Some pointers or short explanation would be great.

Thanks in advance.

Statistics: Posted by luke — Tue Apr 22, 2008 12:15 pm