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I have a tablet that has one USB-C exit. I need to connect power supply and USB to LAN adapter at the same moment. I have bought the only USB-C splitter I could get and it does not work (despite having the chip it does not support on the go USB devices).

I am thinking to reuse the product so it would support my requirements. Can someone suggest a circuit to do that? I am thinking about two possible solutions:

  • complicated solution: a circuit with a chip that truly splits USB channel into two
  • simple solution: connect data between tablet and USB to LAN adapter and connect power supply to both

Is simple solution possible at all?

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    \$\begingroup\$ Tablets and phones take clues from the USB data lines to know the capabilities of the connected charger. It's possible that it wont even go into charge mode with the LAN adapter connected to the USB port. \$\endgroup\$
    – Unimportant
    Dec 29, 2020 at 10:23
  • \$\begingroup\$ what's a "USB-C splitter"? USB is not a splittable bus, so there must be something like a USB hub and a PD controller in that splitter for this to even stand a chance of working. \$\endgroup\$
    – Marcus Müller
    Dec 29, 2020 at 10:43
  • \$\begingroup\$ @Unimportant So it seems I need USB hub chip and PD controller like Marcus Müller suggested? \$\endgroup\$
    – Pygmalion
    Dec 29, 2020 at 10:56
  • \$\begingroup\$ The same problem stands. The device may not switch to charge mode if it's host to a USB hub chip. \$\endgroup\$
    – Unimportant
    Dec 29, 2020 at 10:58
  • \$\begingroup\$ @Unimportant Interestingly enough, that "USB splitter" with a chip allowed charging, it just did not allow OTG to LAN adapter. \$\endgroup\$
    – Pygmalion
    Dec 29, 2020 at 11:04

1 Answer 1

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The problem of expandability of "light" moible devices with only one Type-C port has a standard solution called "docking station". Docking stations usually have a USB hub to expand USB functionality, usually already have a USB-to-LAN device, and can switch roles of USB-C ports, both power role and data role, and also can engage the Display Port direct mode.

To do so, docking stations do have substantial intelligence to negotiate Type-C and Power Delivery contract in right direction (depending on who is powered from AC-DC and power other capabilities), and select correct data role for the portable device.

Initially it is likely that the tablet will come up as USB host and a source of power. After exchanging Power Delivery discovery and capability messages, the power role will be reversed (I assume the dock receives power from some AC-DC adapter, which also could be of Type-C). However, reversing power role of the tablet to "sink" will automatically reverse the data role from "host" to "device". Then it is likely that the dock, knowing that is cannot be "USB host", will offer "data role swap" to the tablet (again over PD messaging channel), and the tablet will accept it and switch into USB host role while continuing to be "power sink". As you might see, no "splitter" or USB2412 simple 2-port hub have the intelligence to do all this negotiations. That's why the docks are a little but pricey. You did save on a cheap tablet, but now you have to pay to expand it.

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