- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
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
Solved! Go to Solution.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
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.
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
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
- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Report Inappropriate Content
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.