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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 TUSB2036 USB hub IC from Texas Instruments 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?

Schematic: enter image description here

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  • \$\begingroup\$ Judging by the labels on the schematic, it looks like you are hooking up 3 GPS modules to your Gumstix. I'm just curious, why would you want to do that? \$\endgroup\$ – Ryan May 19 '12 at 17:48
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  1. It looks like you forgot the 15k pulldown termination resistors on DP[1-3] and DM[1-3], you can see these in the TUSB2036 datasheet in Figure 9 through 11. These resistors are part of the USB specification.

  2. The USB signals can be connected directly to the Gumstix Overo USB connections. The easiest way to answer these type of questions is to look at the schematics for the Gumstix expansion boards, available here: http://pubs.gumstix.com/boards/ .

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    \$\begingroup\$ Hi Ryan, thanks for your comments. I wasn't sure if the pulldown resistors were necessary, I will add them in. I was looking at Tobi board schematic from Gumstix, and it connects the USB lines directly, but I wanted to double check with someone. Finally, I'm using three GPS receiver modules (with long anteannae cables) to test some some differential and RTK GPS features. \$\endgroup\$ – Igor May 20 '12 at 1:29

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