Question: How can you protect the D+/D- lines in CY7C65620 from being permanently damaged by ESD?
For protection on D+/D- lines, you can use protection diode arrays like NUP4201DR2. More information on this device can be found at http://www.onsemi.com/pub_link/Collateral/AND8082-D.PDF. This can be used on both the upstream and the downstream ports of the HUB to ensure protection at both ends.
The USB 2.0 high-speed electrical specification mandates no impedance other than a 90Ω differential impedance between the D+ and D- lines. The aforementioned ESD diodes are designed taking this requirement into consideration.