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HD3SS460: USB Speed drop from USB3 to USB2

Jim CHEN
Expert 4795 points
Part Number: HD3SS460
Other Parts Discussed in Thread: TPS65987

Dear Team,

My customer has one Android USB host which support USB3 Gen1(5G/s). 

On their board there is one Type-C connector which uses HD3SS460 and TPS65987.

When connecting the host to the device their log showed that USB speed start at USB3 Gen1 then drop to USB2 only after about 10~20 seconds.

We check Vcm spec of Android host, its Vcm is from 0 to 2.2V, but HD3SS460 has only from 0 to 2V. Is it the possible root cause that make the speed drop?

From USB3 spec, Vcm is from 0 to 2.2V also, so I would like to know doesn't HD3SS460 follow the spec?

My customer is trying to follow the suggest placement on the EVM user guide.

Please help to clarify the issue and provide your advice.

Thank you.

Regards,

Jim 

  • 0
    TI__Guru 64326 points

    Hi Jim,

    USB 3 spec does not apply to muxes in the USB path. If the Vcm is too high there could be voltage clipping in the data path. You should probe the super speed pairs to understand if this is happening. From your description, there seems to be SI issues that cause data errors and reduce bus speed. You should be able to see a large amount of errors in a USB trace. Can you provide a eye diagram for this system?