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I am planning on providing a system with the option of powering via USB. Now the system will require greater than 100mA, so USB 3.0 interface will need to be used for powering the system. The data transfer via USB will only be capable of interfacing with USB 2.0.

What is the difference between the power lines of USB 2 and 3 and can this impact my data transfer whilst being powered via "USB 3.0". I have read something about the USB 2.0 Data pins being used for powering for USB 3.0B? Not too sure.

TL;DR At the moment i am not sure whether my system will be able to transfer data via the USB 2.0 pins (D+, D-) whilst being powered by USB 3.0 (~900mA). SAME CONNECTOR.

Thanks

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    \$\begingroup\$ How much power do you need? USB2 goes up to 500mA, not 100mA. \$\endgroup\$ – Finbarr Sep 20 '17 at 16:01
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    \$\begingroup\$ USB2.0 specifications allow for up to 500mA current. Officially only after negotiating that current ability, but as far as I know many devices don't bother with that. You might not need USB3, is what I'm saying. Or is the 900mA you mention your current requirement? \$\endgroup\$ – marcelm Sep 20 '17 at 16:02
  • \$\begingroup\$ It should be possible to implement USB 3.0 High Speed with everything from USB 2.0HS except testing. \$\endgroup\$ – user3528438 Sep 20 '17 at 19:06
  • \$\begingroup\$ @user3528438, what do you mean "except testing"? USB2.0 is a full subset of USB3.0, including all test modes. \$\endgroup\$ – Ale..chenski Sep 20 '17 at 20:37
  • \$\begingroup\$ @AliChen Like the 900mA part. \$\endgroup\$ – user3528438 Sep 20 '17 at 20:42
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From an official point of view, if you use a USB3.X Connector you should be able to get USB3.X Functionallity since in the USB Certification you would need to also test the superspeed portion of your device.

If a device is superspeed the D-/D+ lanes are NOT used for power, they are in idle state once USB3.X Traffic is going on.

So if not looking at the official standard, your implementation should work when using High Speed lanes and the Power of the USB3.X. but I would not recommend this !

Another thing I would like to suggest is using a Type-C(tm) connector and looking into the power rating of this, might be more suitable for your specific requirement instead of creating a Half USB3.X the power would depend on the hosts RP configuration(500mA or 1500mA or 3000mA)

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