I am curious, if i am reading the digram correctly, how usb - c can charge a laptop and then with the same port(different time) power a peripheral device(like hard drive.) looking at the pinout it has the data pins (all the tx, rx, and d+/-) and cc for "negotiating" what voltage/amperage to charge at. however it seems that there is only one power pin for both ways. does usb - c send power the device over the same pin(s) it charges on? does each port requires its own ic to control charge and direction? what is vconn?

all help is much appreciated, vesper krate

pinout diagram: enter image description here


closed as unclear what you're asking by Dmitry Grigoryev, Voltage Spike, Wesley Lee, uint128_t, Enric Blanco Apr 27 '17 at 13:15

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  • \$\begingroup\$ This sounds like you plan to plug both the charger and the hard drive in the same USB-C port. This is not possible, USB links are point-to-point, no stars loops or buses allowed. \$\endgroup\$ – Dmitry Grigoryev Apr 19 '17 at 14:40

Yes. It both sends power and receives power over the same Vbus pin. The CC pin is used to determine which way power should initially flow (along with how much current can be sourced), and power is only applied to Vbus once a downward-facing-port detects an appropriate device has been attached. The direction of power flow can be changed later on using the power management protocol, which is a separate communications system sent over the CC pin (this is not supported on all devices).

What sort of IC hardware is required for each port depends on what features that port supports. Very little power management stuff is required if you are just making a simple dedicated peripheral or dedicated host port. If you want to use the new features, such as dual-role ports, and high power capacity, then you'll need to use a quite complicated power switching and control system. There are a few manufacturers who make chips to support this, but they are still not that common.

Lastly, Vconn is used to supply power to electronically marked cables and/or active cables. Electronically marked cables have a microcontroller inside them that can can report the cable's voltage and current capabilities to a port, while active cables have internal buffers for conditioning the super-speed data lines to allow longer cable lengths than would otherwise be possible. Vconn also has some other uses for Alternate Mode accessories (such as analog audio adaptors) but you are best to refer to the spec if you are planning on using these features.

  • 1
    \$\begingroup\$ thank you jon. i am making a laptop with the raspberry pi compute module and would like to use usb c ports for charging and data. the pi is only capable of 2.0 speeds but I prefer the form factor of usb c. have any chip suggestions? thanks for your fantastic reply!! \$\endgroup\$ – Vesperk38 Apr 19 '17 at 19:44
  • \$\begingroup\$ @Vesperk38 Have a look at the TUSB320 for doing the CC line interface. You'll also need something like an AP2552 to control power to the port when in sourcing mode, while a diode can be used to route power when in sinking mode. The spec says you can either toggle between sourcing and sink mode periodically, or have the mode selectable in software. If you want to support battery charging spec you just deal with this like regular USB 2.0 (sense the resistors on the data lines etc). \$\endgroup\$ – Jon Apr 19 '17 at 20:12
  • \$\begingroup\$ thank you so much. was there a spec sheet or data sheet that you read or have you gained this knowledge through experience? if you fond the usb c datasheet i would love to take a look at it. I have searched in vain. thanks for the chips suggestions I will be sure to check them out. thank you so much for all of your help! \$\endgroup\$ – Vesperk38 Apr 20 '17 at 1:26
  • \$\begingroup\$ @Vesperk38 I have been working with USB for a while and was looking into using USB-C dual-role capability on a new product. The information is from the USB spec usb.org/developers/usbtypec \$\endgroup\$ – Jon Apr 20 '17 at 8:47
  • \$\begingroup\$ @Jon, you said that "active cables are used with super-speed interface which requires internal buffers". Could you support your assertion from specifications? AFAIK, Vconn is used only to power CC e-marker chips inside the cable overmold to negotiate power capabilities of the cable, and nothing is said about super-speed buffers. \$\endgroup\$ – Ale..chenski Apr 24 '17 at 0:57

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