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USB2.0 questions

cupoftea

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Hi,
We have a USB Type 2.0 connection coming on to a board, where it connects to a PIC micro. The connector is TE Connectivity 2173157.
Do you believe that all USB2.0 cables on the market, that connect with the above connector, will be shielded cables?

2173157 USB 2.0 connector

Also, would you agree that all USB2.0 connections coming on to a board from a cable, will need a common mode choke to be fitted at the cable entrance point, on the PCB? (in the D+ AND D- lines)

...___...___
Also, the USB2.0 has five connections, D+, D-, VBUS,ID and 0V.
We use a common mode choke for D+ AND D-.
And for VBUS, ID and 0V, would you agree that these need a ferrite bead to be placed in their tracks, right by the connector?
--- Updated ---

....___...___..---...---
This connector......

...is for USB 2.0. It has a metal shell, which is supposed to be connected to circuit 0V. But do you think its best to connect it to circuit 0V via a ferrite bead? (ie, for the purposes of radiated emissions suppression , for passing EN55032 EMC testing)
...---...___...---...___
 
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betwixt

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All USB cables SHOULD be shielded but how well it is achieved depends on the manufacturer, I must add that I don't think I've ever seen un-shielded one although it may be in the form of metallised plastic. The shield should ideally be bonded to a low impedance ground. I'm not sure adding any impedance in line with it is a good idea. A USB cable fitted with a ferrite ring around it would seem a better option for stopping EMC.

Brian
 

betwixt

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I wouldn't say they are cashing in because there are legitimate needs for such devices but equally, I wouldn't suggest they should be fitted 'just in case'. Do consider that common-mode or not, the USB signal frequencies extend into the 10s of MHz so they will inevitably degrade the waveform integrity so some degree. In most instances that wouldn't be noticeable but with long cables or poor quality ones it could cause data failures. They are probably very effective at stopping external RF reaching the USB interface inside a product but not so useful at preventing radiation from USB signal leaking out.

Brian.
 

emresel

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If you have chance, I suggest to use common mode filters.
In my experience in past, i faced emi issue @960Mhz which is 2nd harmonic of USB signal (480Mhz) and those filters helped to improve, since then i get to used place it in designs.
Keep in mind, USB2.0 is bidirectional either host or device can apply signal on bus/cable. Both side can be root cause of any emi issue.
 

cupoftea

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In my experience in past, i faced emi issue @960Mhz which is 2nd harmonic of USB signal (480Mhz) and those filters helped to improve, since then i get to used place it in designs.
Thanks, so i guess it must have been the "stray" diff mode inductance of the common mode choke, and the stray line capacitance that did the filtering for you?
 

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