SMT2 USB connector - does 5V power pin need to be driven?

[eskull]

Hello,

We have a Xilinx VC709 board. We had it plugged into PCIe slot on one computer, and then had the Digilent USB/JTAG interface connected to a second computer to remotely re-program the VC709 BPI flash. This worked fine for a day or two, and then the interface stopped working (Digilent no longer appeared in Vivado HWM, nor in host Win10 Device Man). 

We ordered a new SMT2 and swapped out the failed interface. The VC709 programmer now works correctly.

However, to hopefully prevent this happening again (we must have had a ground loop...) we would like to purchase an in-line USB isolator. One we are considering does not drive the 5V line on the USB cable, so that line will be 0V at the SMT2 UBS connector input. 

My question - by what means does the SMT2 sense connection to Vivado HWM? Is it via detection of the USB 5V line? 

In other words, if the USB cable 5Vpin is 0V, will the SMT2  still enumerate to the host (i.e., operate correctly)?

 

Thank you.

[JColvin]

Hi @eskull,

I heard back from one of our design engineers and learned that the IC's present on both the SMT1 and SMT2 are powered from the 3.3V and VREF pins and not VBUS (which isn't connected to anything on the module) so using a USB isolator that does not provide 5V power will be fine.

Thanks,
JColvin