HD3SS3212-Q1: what is the function of hd3ss3212-q1 capacitor?

Please refer to USB3.0 spec, the AC coupling capacitor is required by the USB3.0 spec for couple reasons.
1. To change the DC bias level when interconnecting logic families with different switching thresholds.
2. To provide a removable interface that may be shorted to ground without damaging the output drivers.
3. When combined with differential signaling and transformer coupling, to connect boxes without requiring any DC connection between the two product chassis.

The spec defines the caps to be min of 75nF and max of 265nF, typical value is 100nF.

There is a ECO that AC coupling caps is optional on the RX, the value is min 297nF and max of 363nF, typical value is 330nF.

Thanks
David