USB-C connector 'reversible' power pins ?!

[bob4bvm]

Trying to get my head around the USB-C power delivery...
I am powering an ESP32 via the port and just discovered that the cable plugs in either way !
Moreover, the device accepts the power and operates normally in either case...

I made the power cable by cutting the "C" end off a cheap USB C cable and attaching what i measured as being the V+ and Gnd wires to my 5V supply (battery sourced), after measuring the 5V polarity of the original cable from the USB-A (power source) end.
Being careful to mark the orientation of the C-end connector to maintain polarity. I was then surprised to find that the C plug will insert in either direction, which to my mind should swap the 5V +/- connection; and even more surprised to see that the ESP32 runs fine either way.

I read a bit on the USB C interface and it seems there is more going on that meets the eye. I wonder how that works when the cheap cable i butchered up has only 4 wires from the source end, 2 outside ones carrying 5V & Gnd, and 2 smaller center wires which appear to be data lines

Cheers
Bob

 

[jpanhalt]

Here's a link to the complete USB Type C standard:

https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdf

Page 31, Figure 2.2 shows the plug. Note that the power pins (and others) are symmetrical regardless of how the plug is inserted.

 

[bob4bvm]

Thanks for your reply and the interesting spec doc !

I guess the 4-wire USB A end must do some kind of fanout to more pins at the C end. I would term my app a "captive" cable as defined in the doc, since i am just hard-wiring to 2 power conductors there to the 5V source

Seems like alot of magic going on in that tiny USB-C plug !

Bob