TUSB4020BI: PCB single-ended impedance of USB 2. 0 data differential pair (D+ D-)

Olan Way

Part Number: TUSB4020BI

Our PCB single-ended impedance of USB 2.0 data differential pair (D+ D-) is 65 ohms, and the differential impedance is 90 ohms.

Is this OK?

If not OK, what symptoms can we expect?

over 7 years ago

0 Jorge Llamas (SWAT) over 7 years ago

TI__Expert 7395 points

Hello Olan,

If your odd/single-ended impedance is 65 ohms in both D+ and D-, then your differential impedance should be 130 ohms.

Having an impedance mismatch would produce reflections on your HS differential channel.

As defined by the USB2.0 spec, the impedance of each output/driver must be 45 Ω ±10%.

Regards,
Jorge.

0 Olan Way over 7 years ago in reply to Jorge Llamas (SWAT)

Prodigy 190 points

Hi Jorge,
Thank you for taking time to answer my question.
Can you please comment on this USB.org Q and A, item 6:
www.usb.org/.../usbfaq

Olan

0 Jorge Llamas (SWAT) over 7 years ago in reply to Olan Way

TI__Expert 7395 points

Olan,

That comment may be referring to common mode impedance, not odd impedance.

I would recommend sticking to the USB specification. Check section 7.1 of the USB 2.0 spec.

Regards,
Jorge

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TUSB4020BI: PCB single-ended impedance of USB 2. 0 data differential pair (D+ D-)