CY7C65634-48AXF (HX2VL) USB hub doesn't work when connected to USB-C adapter on Mac

[Anonymous]

I have a board with an integrated USB hub (CY7C65634-48AXF, and 2 peripherals on-board.  The device has a standard (i.e. the large one) USB-B connector (for mechanical robust-ness), The design has been working flawlessly, until a customer connected a standard USB-A to USB-B cable to a USB-A to USB-C adapter, then plugged that USB-C adapter into a modern Mac Mini's USB-C port.

Here's a diagram to explain the issue:

I've seen that if I first plug the USB A to C adapter into the computer, the VBUS is 5V, and everything works as expected.  But if I first plug the adapter onto the cable, then the adapter into the Mac, VBUS never goes high.

This is a self-powered CY7C65634-48AXF.

Is this a known problem?  Any solutions?

Thanks,

-Caleb

[Sananya_14]

Hello Caleb,

We havent seen this issue before.

-Please attach USB traces using a USB hardware analyzer during the hub enumeration if possible.

-In the failure case, does VBUS appear if you assert Reset on the hub?

-Could you also try the same sequence using a HX2VL DVK if you have one?

Best Regards,

Sananya

[Anonymous · Accepted solution]

Ah!  I believe I have found the problem.  I used a uni-directional TVS diode on the data lines to VBUS.   The problem is that VBUS is also used to perform reset on the USB hub.  With a self-powered USB hub, the data lines are pulled high, and in this case that means that the VBUS is pulled high (well, to an indeterminate 2.0 - 2.4V) when the USB cable is un-plugged.  In this case, the Mac host is interpreting the vbus signal as an SRP data-line pulse, and it all goes down hill from there.

I see your recommended schematic has bidirectional TVS diodes. 

I pulled the TVS diode off of the board and everything worked without issues.

That's an easy fix for the next rev.