TUSB1042I: AC Coupling Capacitors

Marcis Greitans

Part Number: TUSB1042I

Dear TI,

In Figures 19 and 20 in the TUSB1042I datasheet AC coupling capacitors have been placed on the SSRX and SSTX pins. However, in Figure 24 they have only been placed on the SSRX pins. What is the correct way to place the AC coupling capacitors? Is the AC coupling capacitor placement independent of the data role of the port (DFP, UFP, DRD)?

Thanks!

over 4 years ago

0 David (ASIC) Liu over 4 years ago

TI__Guru**** 152496 points

Hi,

USB Spec defines each differential link is AC-coupled with capacitors located on the transmitter side of the differential link. Figure 24 shows the capacitor being placed on the transmitter side of the TUSB1042 and assumes that the capacitor is also being placed on the transmitter side of the host, same as Figure 19 and 20.

Thanks

David

0 Malik Barton57 over 4 years ago

TI__Guru 64326 points

Hi Marcis,

AC coupling in independent of port role and both implementations are acceptable. There will always be AC coupling between USB Host and TUSB1042I on both TX and RX. In between the connector and TUSB1042I, it is recommended the 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 a redriver to USB connector. Only AC coupling with TX1/2 with 220nF is also okay.

0 Marcis Greitans over 4 years ago in reply to Malik Barton57

Prodigy 240 points

Hi Malik,

Could you please tell me where did you get the 220nF and 330nF values? Is there an application note or some other document where I could read more about this?

Thanks!

0 Malik Barton57 over 4 years ago in reply to Marcis Greitans

TI__Guru 64326 points

Hi Marcis,

These numbers come from the USB 3.2 spec. See the below image for reference.

Interface

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TUSB1042I: AC Coupling Capacitors