USB in two connectors at the same time

[ctzof]

Hello,

I am building a new PCIe board with an Atmel microcontroller. The microcontroller has an integrated USB transceiver inside. The D+ and D- signals currently are connected to an USB-B connector. I want to connect these pins also to PCIe usb pins so the board can be connected via USB throufg PCIe by removing the connector and opposite. The problem is that if I draw two differential lines one for the connector and one for the PCIe this is going to affect the impedance of the line. For example by removing the USB-B connector the one end of the two differential lines its going to be an open. Any suggestions on how to do that...

 

[Dan Mills]

Pair of zero ohm links right behind where the usb socket would go, and fit one or the other at build time (the few mm long stub should not be an issue).

I assume we are talking one of the various small format cards here as standard PCIe does not have a USB link.

Regards, Dan.

 

[ctzof]

Pair of zero ohm links right behind where the usb socket would go, and fit one or the other at build time (the few mm long stub should not be an issue).

I assume we are talking one of the various small format cards here as standard PCIe does not have a USB link.

Regards, Dan.

Yes is a half mini PCIe card. I thought too using zero ohm resistor but the problem is that both connector and PCIe pins are aay from the chip and this creates long stubs. The other problem is that the connector is located up and the PCIe pins down so when you using zero ohm resistors the lines cross cause they have certain polarity.

 

[ads-ee]

You could try routing it like this:


Either the top 0 ohm or the bottom 0 ohm pair are populated depending on which connector you have installed.

 

[ctzof]

You could try routing it like this:
View attachment 109164

Either the top 0 ohm or the bottom 0 ohm pair are populated depending on which connector you have installed.

Thanks. That could be a solution. I suppose I have to add two more vias which can not be seen in the picture cause the chip is on the top right?

 

[FvM]

Atmel controller means full speed (12 MBit/s) USB, right? You don't need to worry about open stubs in this case.

 

[ads-ee]

My picture is looking at both the top and bottom of the board from the same side. You did say one connector was on the top and one was on the opposite side of the board (bottom)?

Sorry I didn't make that completely clear from the drawing. Hard to draw 3D in a 2D drawing environment. ;-)

Considering it's only full speed USB you could probably forget about the 0 ohm resistors as you don't need a very long traces to go from the vias to the connector on the opposite side of the board. Should be well under a 1 inch stub.

Regards

 

[ctzof]

My picture is looking at both the top and bottom of the board from the same side. You did say one connector was on the top and one was on the opposite side of the board (bottom)?

Sorry I didn't make that completely clear from the drawing. Hard to draw 3D in a 2D drawing environment. ;-)

Considering it's only full speed USB you could probably forget about the 0 ohm resistors as you don't need a very long traces to go from the vias to the connector on the opposite side of the board. Should be well under a 1 inch stub.

Regards

The connector is through hole so either top and bottom. The PCIe pins are on top. Anyway I understand what you mean. The thing is that plans are changed and we don't need this dual USB connection anymore. Thanks for the help and the drawing :thumbsup: