SparkFun Forums

[gbmidi]

So I'm building a USB Midi interface and have encountered some dropout/non-responsive usb issues. It seems I need to pay more attention to routing the D- and D+ lines. Here are some design ideas I have so far to address the issues:

-Route D- and D+ without using vias
-Make D- and D+ traces as short as possible
-Make D- and D+ traces large (0.016")
-Do not route over transitions in ground/power planes
-Route D- and D+ parallel to each other
-Create a large isolation region around D- and D+ from ground plane

What does everyone think? Is there more I can do?

[linuxdev]

You might find this document useful:
http://docs.toradex.com/101123-apalis-a ... -guide.pdf
...this is about how to design boards surrounding SoCs, and includes information specific to USB (though this is just a small subset of the document).

What it comes down to is that traces essentially become antenna transmission lines...there is an advantage to D+/D- being the same total length (each turn increases length on one trace relative to another...so put a balancing turn in the opposite direction), advantages exist for shorter traces, and capacitance between traces changes impedance (you might for example find the chip manufacturers specify impedance of 50 ohm or 90 ohm, just like an antenna). Ask yourself what you'd do if this were a big transmitter antenna's transmission line.