20V Power-Only USB-C?  (How is it compliant?) - Page 1
Forum section: electronics / projects

author: Dave8266
author_rank: Contributor
timestamp: March 09, 2021, 03:42:49 am
content: I recently looked into adding a USB-C receptacle to a project, solely to provide power and with no need for data connectivity.In the process I came across these "Power Only" jacks, which are cheaper (and easier to use), as they have the data pins removed, with only power and ground pins remaining.For example, the "UJC-HP-G-SMT-TR", from CUI Devices. (https://www.cuidevices.com/blog/an-introduction-to-power-only-usb-type-c-connectors)Curiously though, these parts are advertised with 60W and 100W ratings (20V @ 3A or 5A)....But wouldn't it be a violation of the USB spec to simply blast 20V on the power pins without having the data pins negotiate the USB-PD transition from 5V to 20V?

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 09, 2021, 03:55:31 am
content: I have seen USB-C jacks that are power only with the CC lines brought out to connect to the application circuit, but a USB-C connector without the CC lines at all is dodgy technology.

author: ataradov
author_rank: Super Contributor
timestamp: March 09, 2021, 04:20:50 am
content: B5 and A5 are CCx pins. This connector is fine. It has the absolute minimum number of pins necessary to be compliant and useful.

author: sleemanj
author_rank: Super Contributor
timestamp: March 09, 2021, 05:37:15 am
content: Yes, without data there is no way for the negotiation to occur, so, 5v is it unless you throw standards out the window. They also allude to this on that page you linked..."Please note that since the data transfer pins have been removed,the USB 3.0 power negotiation process does not occur, in which case the charging device will revert to the USB standard power transfer rate of 5 V and 1 A. For all other applications, the connector will function like any other power jack and the charging will be governed by the adapter/charging circuit."The only thing that the CC pins provide is to advertise the current from the DFP (at 5v) and to detect cable orientation (flipped or unflipped), they do not provide a means to select anything, let alone voltage.Edit: I'm, actually not so sure now I think I might be out of date or entirely mistaken here. USB PD can happen over VBus and CC only, maybe it was only USB 3 that needed more. USB all got way too complicated.

author: ConKbot
author_rank: Super Contributor
timestamp: March 09, 2021, 02:31:47 pm
content: I suspect I goes along the lines of 'it's a USB power bank, why would I add a USB micro just to tell the user via billboard this is a power bank, don't expect it to do anything besides charge when hooked up to a PC'Usb 3.2 gen 2 mark 35 mod 15 revision 4 for Type C is so bloated, can you really blame people for ignoring extraneous fluff, when before it was "add connector, get 5v"

author: TimNJ
author_rank: Super Contributor
timestamp: March 09, 2021, 06:00:43 pm
content: USB PD negotiates power over the the CC line in the USB Type-C to Type-C cable. There's only 1 CC wire. The signal is referenced to the ground conductor of the cable. The output connector at the power adapter end has 2 CC pins. They are positioned such that the CC wire in the cable is connected through to the load/device, even when the Type-C plug is inserted "up-side down" at the power adapter.For a "smart" power-only application, usually you'd want VBUS + GND + CC + (D+) + (D-) :"Type-C current" is up to 3A @ 5V. The load checks the value a pull-up resistor on CC line. (Does not need D+ or D-). Depending on the value of the resistor, it determines the current capability of the source. No serial communication is needed for this, just a relatively simple controller which can handle this logic.USB PD is up to 5A @ 20V. The load and source communicate over CC with the serial protocol, and agree to a voltage/current.USB BC1.2 (+ old Apple, Samsung, Sony standards) use the D+/D- line, usually checking for some voltage.Qualcomm QuickCharge uses D+/D-. I think the Huawei and Samsung fast charge standards also use D+/D-.So, if you don't care about the D+/D- protocols, you don't need to have D+/D- pins. But generally, yes, you want at least CC. CUI's connector is really just a barrel plug replacement, for some products which want the look and feel of a new modern product, but don't actually want to include the controller/management circuitry. I'm not sure how crazy it is other than getting some confused users when a 20V system (using this connector) doesn't work when someone plugs in their 9V max USB PD power adapter.