TUSB7320 DC blocking Capacitors for USB_SSTXP_DN1 and USB SSRXP_DN1 diff pair

Philip Hsueh91

Other Parts Discussed in Thread: TUSB7320, TUSB7340

Hi,

We currently are using TUSB7320 and with the wrong DC blocking capacitors placed on the USB_SSRXP_DN1 side. But we check the eye diagram, it passed USB3.0. I am wondering if your chip TUSB7320 has an internal capacitor built in?

We tried both cases with caps on TX side only or RX side only. Both cases working for us. I am wondering why?

Can you explain?

Thanks,

Philip

over 8 years ago

0 Elias Villegas M. over 8 years ago

TI__Guru* 76130 points

Hello,
Can you put in a block diagram your set up?
When you say "it is working" you mean the eye diagram looks good or the USB device works properly?
The tUSB7340 does not have internal dc-bloking capacitors.
Regards

0 Philip Hsueh91 over 8 years ago in reply to Elias Villegas M.

Prodigy 30 points

Yes, the eye diagrams says Passed. I have attached the diagram in this message. I am wondering if we don't put the DC blocking capacitor in, will the USB3.0 still work?

Thanks,

PhilipUSB3 Tx.pdf

0 Elias Villegas M. over 8 years ago in reply to Philip Hsueh91

TI__Guru* 76130 points

You need to place the DC blocking caps on the super speed TX lines, this is required by the spec and you may have interoperabillity issues if you don't put them.
I think your lab equipment is compensating the DC level no matter if you put the caps or not.
Regards

0 Philip Hsueh91 over 8 years ago in reply to Elias Villegas M.

Prodigy 30 points

Elias,

I understood what you said and suspected the test equipment might have the DC blocking caps, too. If there is no DC blocking cap in place during the normal operation, USB 3.0 should fail. But what bothers me is USB3.0 is working and we don't see errors with or without the caps. How could it happen?

Philip

Interface

Interface forum

TUSB7320 DC blocking Capacitors for USB_SSTXP_DN1 and USB SSRXP_DN1 diff pair