TUSB7320: Routing TUSB7320

juanma cc

Part Number: TUSB7320

Hi everyone, I have routed TUSB7320 controller like this:

Blue polygons are power polygons, I have read the Design Layout Guidelines and says that: "Don't route signals over split planes". I understand that polygon is not the same that split plane, Will my design work or there is some problem?

Other question, When I had length matching, I have kept on mind the internal length mismatching, that is the way, isn't it?

Thank you so much!

over 2 years ago

0 Malik Barton57 over 2 years ago

TI__Guru 64326 points

Hi,

I do not recommend routing a power trace over the pins of the USB connector here. Even if the signals are on different layers.

No sure I understand your question on length matching? For USB 3 there is only a intra-pair skew (length matching) requirement. Reference section 3.3 High-Speed Signal Trace Length Matching in High-Speed Layout Guidelines for Signal Conditioners and USB Hubs

0 juanma cc over 2 years ago in reply to Malik Barton57

Prodigy 140 points

But, What does it mean "never route signals over split reference plane"? If a signal is routed over power plane on bottom layer (my stack layer is top-gnd-power-bottom) will it be any problem? Or Will the problem come when I route a signal over space between two planes?

0 Malik Barton57 over 2 years ago in reply to juanma cc

TI__Guru 64326 points

Hi,

Refer to Figure 5. Routing Across a Split Plane for a example of what this looks like. I do not recommend using the power plane as your signal reference. If you are using the VCC plane as the reference plane please refer to Figure 11. VCC Reference Plane.

High-Speed Layout Guidelines for Signal Conditioners and USB

0 juanma cc over 2 years ago in reply to Malik Barton57

Prodigy 140 points

I don't understand what you mean with Reference Plane, I don't have any ground on my power layer. My layer stack up is Top (signal) - GND -Power -Bottom(signal). Do you want to say that i shouldn't route on Bottom layer?

0 Malik Barton57 over 2 years ago in reply to juanma cc

TI__Guru 64326 points

No, the differential path will reference the closet solid plane (lowest impedance path for the return current. This is known as the reference plane and can be the power plane along as it is the closet path for the return current. Power plane is used as reference plane in your case and this is not recommended. If possible you can add layers to your board and in between power and bottom layer add a solid ground plane.

0 juanma cc over 2 years ago in reply to Malik Barton57

Prodigy 140 points

Thank you so much Malik, the other option is routing all on the top layer, or use PWR plane as GND and move power to top and bottom layers ,right?

Other fast question, If I add layers, for what I should the 3rd layer? I mean, the best stack up should be: Top-GND-PWR-PWR-GND-Bottom?

+1 Malik Barton57 over 2 years ago in reply to juanma cc

TI__Guru 64326 points

Correct both are options available to you but the changing the stack-up to order you mentioned, Top-GND-PWR-PWR-GND-Bottom, would be the best option.

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TUSB7320: Routing TUSB7320