[SI-LIST] Re: High speed USB cable

[olaney@xxxxxxxx]

Fixing emissions at the cable is not the first line of defense.  The
ferrite should be inside the USB peripheral -- an internal CM choke at
the connector.  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 pass without ferrite on the cable.

Orin

On Fri, 18 Jan 2008 06:32:53 +0530 (IST) Bharathkumar Raju
<bharathrajupcb@xxxxxxxxxxx> 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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