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USB Superspeed Peripherals

Anonymous
Not applicable

We are using a USB TypeC mux with the FX3 (CYUSB3014BZX).  The TypeC mux requires a bias of 0-2VDC on the super-speed signals, specifically the RX pair.  What is the bias or common mode voltage on the SSTX+/- and SSRX+/- signals of the FX3?

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Moderator
Moderator

Andrew,

From FX3 side, TX will bias its pair according to Superspeed spec. This can vary from 0 - 2 VDC

RX will not bias its pair and will expect a bias from the other end. Bias from TX should propogate through the Mux.

You can choose to AC couple the RX line in order to provide local bias. The capacitor footprints can be filled with 0 ohm resistors if not needed.

Regards,

Rajath

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Moderator
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Hello,

On FX3 SSTX+/-  side, we are specifying AC coupling capacitors inline to block DC bias.

But it will not prevent AC common mode signals.

Can you please provide the datasheet of the Tye-C Mux? Is the bias/common mode voltage required on input side or output side of the mux?

Regards,

Rajath

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Anonymous
Not applicable

The device is a HD3SS3220.  The datasheet is at the following link.

HD3SS3220 10Gbps USB 3.1 Type-C 2:1 Mux with DRP Controller | TI.com

The specific requirement is in Table 13 on page 27.

pastedImage_1.png

We have measured the DC voltage of the SSTX and SSRX signals on the FX3 DVK.  We believe the common mode voltage of the SSRX signals is 0V or possibly 300mV.  We thought we would see 1.2V or 600mV.  The common mode voltage of the FX3 side of the AC coupling capacitors looks like it is 600mV.

Thank you

Andrew

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Anonymous
Not applicable

Can you just tell me what the bias or common mode voltage is on the following superspeed pairs?  If you are unable to answer the question, we will AC couple everything and provide a local bias for the mux.  At these signalling rates it is not desirable to have extra components and vias that are not necessary.

SSRX+/SSRX-

SSTX+/SSRX-

Thanks,

Andrew

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Moderator
Moderator

Andrew,

From FX3 side, TX will bias its pair according to Superspeed spec. This can vary from 0 - 2 VDC

RX will not bias its pair and will expect a bias from the other end. Bias from TX should propogate through the Mux.

You can choose to AC couple the RX line in order to provide local bias. The capacitor footprints can be filled with 0 ohm resistors if not needed.

Regards,

Rajath

View solution in original post

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