Does the USB signals need to be level shifted?

  Atilans 04:56 20 Oct 2017

I'm designing an expansion board for a Gumstix Overo IronStorm COM (Computer on Module). I need to connect three different USB devices to the Gumstix acting as a USB Host - all devices and the Gumstix will be on the same PCB. I'm using the TI's TUSB2036 USB hub IC to do the job.

I think I've figured it out, but would appreciate any comments on the design below from any more experienced members who have used the gumstix and/or USB hubs before. All devices (the hub and three downstream USB devices) are self-powered. The downstream USB devices need to see 3V3 on the USB VBUS line to initiate their USB subsystems; that is why the PMIC input is 3V3. So, any comments on the attached schematic?

Secondly, the Gumstix documentation explicitly states that all logic is 1.8V. Does this mean that even the USB signals need to be level shifted before connecting them to the Gumstix? I'm pretty sure I should be able to connect the TUSB2036 upstream port (DM0 and DP0) directly to the Gumstix USB Host lines. Is this correct?

Here are the schematics:

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