I have been wanting to DIY a y-USB cable separating the power from data. However, there are so many questions to get answered......
1. What if ..... One input end is power only and the the other input end is power/data?
2. Or ..... One input end is power only and the the other input end is data only?
3. How do you handle grounding?
My research in learning USB communications has led me to download (and read, buti na lang may tablet) technotes, white papers, design guidelines from manufacturers that seems to have one thing in common, grounding is not a major part of the problem, nor is routing of the data/power lines. The main issue that needs to be addressed is shielding, more specifically EMI shielding as this is the one nuisance that would affect high speed USB communications.
I also learned that the common knowledge of using ferrite cores in the cables neither help nor do anything in terms of EMI shielding as these were common-mode approaches.
If you'll notice iFi's implementation was to couple the data via "impedance matching" which I implemented in my prototype.
So many other questions on how to approach the assembly.......
What I learned in life is that most questions have answers, getting the right one is the bummer of it all. The good news is we now know the science and have the means to implement it, it's just a matter of time.