AC Coupling Caps On SoM Pro Carrier Board FFC-4P

CalebBergquist

Hi all!

I had a question about the AC coupling capacitors on the FFC-4P SoM PRO carrier board.

I see in the SoM Pro documentation, that AC coupling capacitors are onboard the SoM Pro for SSTX P/N

And I'm assuming the circled is the onboard-SoM AC coupling caps:

I'm attempting to make a Som Pro carrier board, and was wondering- since the SoM Pro already has TX AC coupling caps on the SoM itself, are the AC coupling caps on the Som Pro carrier board required? Or can I wire TX lines straight to the SoM after the mux (without AC coupling caps)?

I'm intending to use a passive mux on my board for context (HD3SS3212IRKSR)

jakaskerl

CalebBergquist
The SoM Pro already includes AC-coupling capacitors on the USB 3 TX lines, so you don’t need to add them on your carrier board. You can route the TX pairs directly from the SoM through your HD3SS3212 mux to the connector.
Thanks,
Jaka

CalebBergquist

Thank you for confirming!

Follow up question just out of curiosity. It the SoM Pro module already has AC coupling caps on TX, why does the FFC-4P SoM Pro carrier board double up and also put AC coupling caps on the TX lines?

Is it because the mux used on the carrier board is an active/redriver mux? The schematic shows a generic "USB Type C Switch" for the part in the FFC-4P schematic, or I would have confirmed on my own