TUSB9261: Layout Impedance Check

Hi, 

Each differential pair’s traces should be routed with 90-Ω, ±15% differential impedance. So the 85ohm impedance is still within the TUSB9261 impedance tolerance range.

Thanks

David

Hi There,

               The datasheet needs (103.5 ~ 78.26)-Ω = 90-Ω±15% ,but the PCB manufacture can only support 85-Ω ±10%, so the impedance will be (93.5~77.27)-Ω = 85-Ω±10%, maybe this will have some problem!

Hi,

The PCB manufacturer can specify the tolerance, 5%, 10%, or 15%, but they should able to achieve the 90ohm impedance by doing the impedance calculation based on the trace width/height, isolation high, dielectric constant, etc. Can you ask the PCB manufacturer to provide you a coupon board with the impedance measurement result?

Even with 85ohm +/10%, you are only off slightly, so I do not see this as a significant issue.

Thanks

David 

Hi David,

               So the  85ohm +/10% impedance can meet the TUSB9261 Super Speed Trace (SSRX+/- & SSTX+/-) impedance requirement ?

Thanks

Hi,

1. Please work with the board shop to achieve 90ohm differential impedance by changing the trace width and height. I don't understand why the board shop can only achieve with 85ohm differential impedance given that they should able to control the trace width and height.

2. 85ohm +/10% impedance is slightly off from the TUSB9261 impedance requirement, but I don't see this as a significant issue

3. If the impedance is a concern, you could ask the board shop to provide you the coupon board with the impedance measurement result and only use the board that met the TUSB9261 impedance requirement.

Thanks

David

Hi David,

              The Board manufacture can offer the 90ohm, but the cpu datasheet says the USB impedance need to be set to 85ohm +/-10% !!!!!!