TUSB8020B: using an external clock source

Hi Team,

The datasheet shows the following.
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8.3.4.2 Input Clock Requirements
When using an external clock source such as an oscillator, the reference clock should have a ±100 PPM or better frequency stability and have less than 50-ps absolute peak-to-peak jitter or less than 25-ps peak-to-peak jitter after applying the USB 3.0 jitter transfer function. XI should be tied to the 1.8-V clock source and XO should be left floating.
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Is there a requirement of VIH / VIL when using 1.8V clock source?

Best Regards,
Yaita