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HD3SS3212: AC Coupling Caps Placement

Part Number: HD3SS3212

The datasheet seems to jump around regarding which side of the MUX should have the AC caps on the SSTX lines.

Figure 7 shows the caps between the MUX and a USB-C connector to support flipping.

But then Fig. 8 and 11 turn around and show the caps between the device and the MUX, not between the MUX and connector.

Is there any affect on the EYE diagram with having the caps in one configuration vs the other?

I understand having caps on both sides means we need a biasing voltage - but if caps are only on one side of the MUX, which side is best, and why?


  • Hi,

    Effect on the eye diagram will be largely the same if only one set of AC coupling caps is used. The reason AC coupling between an IC and USB-C connector is recommended is to protect that IC from common mode voltage outside of it's own specification. Since we do not know ahead of time what can be connected to the USB-C port, this helps prevent damage to the part. 

    TX1/2 should be AC coupled with 220nF and RX1/2 should be AC coupled with 330 nF. This is highly recommended when AC coupling to a USB-C connector.