USB differential signals

[Rajinder]

Hi all,
I am laying out a board that has a USB connector. It will be used for USB 2.0.

From the connector the signals route out to a TVs clamp then to a FTDI chip. However the D+ and D- signals cross over when they go to the FDTI chip to get to the appropriate pins. How can I overcome this? Are there any solutions?
I have a 2 layer PCB, signals/power on top and GND plane on the bottom layer.
Also how can I find out the width of the D+/D-tracks required for a 2 layer PCB.

Thanks in advance.

 

[Harald Kapp]

However the D+ and D- signals cross over

That's what a 2-layer pcb is for. Let them cross on separate layers.

Also how can I find out the width of the D+/D-tracks required for a 2 layer PCB.

Use the minimum trace width. There is not a lot of current going through these data lines. Between USB connector and TVS diodes make the traces maybe wider, as wide as the available pcb real estate allows. This helps carry high peak currents to the tvs diodes in case of a surge.

 

[Rajinder]

Thanks. I have resolved the issue.
I decided to go with a 4 layer PcB as below:

• 4 layer board (from the top: signal, ground, VCC,signal)

I have used some online impedance calculators, 0.2mm track width and spacing is what I need to get 90 ohm impedance. My concern is that the traces don't stay evenly spaced the whole time since they run through the parallel caps and series resistors before hitting the FTDI chip. The Top is the Micro usb. Is this going to be a problem at 480MHz? USB 2.0? The overall track length is around 12mm.

I will share the impedance calculator. The only option can think of is using a V shape track to come from the Micro USB and RC components.
Still the track space will vary. Any suggestions please.