[SI-LIST] High speed USB Query

Hello All,
We are testing Fast Transients (IEC 61000 4-4) through capacitive coupling,
on USB High speed lines (480Mbps).Requirements like differential impedance
(90), transient protection have been maintained.
Results:
1. Our device re-enumerates during testing. But there is no data corruption.
But the main processor is not reset. Re-enumeration is not accepted in our
application.
2. Using a common mode choke (Recommended in INTEL guidelines for High speed
USB Design) on the data lines, test was successfull.

But many are saying that it is not advisable to use chokes. Using chokes may
cause even enumeration problems (i.e when 2 devices are connected, one with
choke another without, the devices may not enumerate)

Any experience on EMI compliance with USB lines? Anybody has faced
enumeration problems when multiple devices (with chokes) are connected?
Please share.

Regards
Mani


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