[SI-LIST] Re: High speed USB cable
- From: "Clewell, Craig" <Cclewell@xxxxxxxxxxxxx>
- To: "bharathrajupcb@xxxxxxxxxxx" <bharathrajupcb@xxxxxxxxxxx>
- Date: Fri, 18 Jan 2008 08:32:24 -0500
In addition, note that the USB cable does not have to meet CISPR Class B r=
equirements to be able to use the logo. For your particular application it=
may need to pass, but the USB spec only requires a shielding effectiveness=
test. Furthermore, I know for a fact that a USB cable can meet CISPR Cla=
ss C requirements with a properly shielded cable, and attention to the term=
inations since I have done so. The "system" is reliant on not only the cab=
le, but the termination to the cable. In other words, the same cable can b=
e used in 2 different "systems" and only pass in one due to differences in =
the terminations. The closer you get to the 360 degree termination the bet=
ter. Pay attention to the termination of the shield. Orin alluded to your=
fist line of defense which should be looking at the source, and how the en=
ergy is getting out.
Craig
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On=
Behalf Of olaney@xxxxxxxx
Sent: Thursday, January 17, 2008 21:41
To: bharathrajupcb@xxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: High speed USB cable
Fixing emissions at the cable is not the first line of defense. The ferrit=
e should be inside the USB peripheral -- an internal CM choke at the connec=
tor. If you are failing with high quality, properly shielded cable and can=
't add a ferrite externally, then there is nothing else to do for the cable=
-- you have to fix the device. And yes, a properly designed device will p=
ass without ferrite on the cable.
Orin
On Fri, 18 Jan 2008 06:32:53 +0530 (IST) Bharathkumar Raju <bharathrajupcb@=
yahoo.co.in> writes:
> What charecteristics the high speed USB cable must have to pass FCC
> Class B radiated emissions? We cannot add a ferrite core to the cable
> to supress the emissions. The device is a self powered high speed (480
> MHz) USB device. From various testings it is established that the CM
> curent flowing through the D+ & D- conductors of the USB cable causing
> the failures in the radiated emission testing. The tests also
> established that the CM current flowing through the 5.0 volts +ve &
> -ve conductors of the USB cable is not at all contributing for the
> emissions.
> Is it feasible to have a high speed USB bus powered
> device with 1.5 m long USB cable to meet FCC / CISPR ClassB radiated
> emission limits (without a ferrite core attached to it).
> Bharath
>
> PS : I hope this question is appropriate for this forum..
>
>
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