What’s the role of CC pin in Type-C solution

What’s the role of CC pin in Type-C solution

For the USB Type-C solution, two pins on the connector, CC1 and CC2, are used to establish and manage the Source-to-Sink connection.

Functionally, the configuration channel is used to serve the following purposes.

• Detect attach of USB ports, e.g. a Source to a Sink

• Resolve cable orientation and twist connections to establish USB data bus routing

• Establish data roles between two attached ports

• Discover and configure VBUS: USB Type-C Current modes or USB Power Delivery

• Configure VCONN

• Discover and configure optional Alternate and Accessory modes

1. Detect attach of USB ports, e.g. a Source to a Sink

The general concept for setting up a valid connection between a Source and Sink is based on being able to detect terminations residing in the product being attached.

To aid in defining the functional behavior of CC, a pull-up (Rp) and pull-down (Rd) termination model is used – actual implementation in hosts and devices may vary.

Initially, a Source exposes independent Rp terminations on its CC1 and CC2 pins, and a Sink exposes independent Rd terminations on its CC1 and CC2 pins, the Source-to-Sink combination of this circuit configuration represents a valid connection.

To detect this, the Source monitors CC1 and CC2 for a voltage lower than its unterminated voltage. This indicates that either a Sink, a powered cable, or a Sink connected via a powered cable has been attached.

2. Resolve cable orientation and twist connections to establish USB data bus routing

Only one CC pin is connected through the cable to establish signal orientation and the other CC pin is repurposed as VCONN for powering electronics in the USB Type-C plug.

To establish the proper routing of the active USB data bus from host to device, the standard USB Type-C cable is wired such that a single CC wire is position aligned with the first USB SuperSpeed signal pairs (SSTXp1/SSTXn1 and SSRXp1/SSRXn1) – in this way, the CC wire and USB SuperSpeed data bus wires that are used for signaling within the cable track with regard to the orientation and twist of the cable.

3. Establish data roles between two attached ports

By being able to detect which of the CC pins (CC1 or CC2) at the receptacle is terminated by the device, the host is able to determine which SuperSpeed USB signals are to be used for the connection and the host can use this to control the functional switch for routing the SuperSpeed USB signal pairs.

Similarly in the device, detecting which of the CC pins at the receptacle is terminated by the host allows the device to control the functional switch that routes its SuperSpeed USB signal pairs.

4. Configure VCONN

The electronically marked cables provides a method to determine the characteristics of the cable, e.g. its current carrying capability, its performance, vendor identification, etc. And the powered cable should expose Ra on its VCONN pin(the other CC pin), the source will source VCONN when Ra is detected.

5. Discover and configure VBUS

The Source will adjusts Rp (or current source) to advertise which current levels (default/1.5A/3A) it supports. The value of Rp establishes a voltage (vRd) on CC that is used by the Sink to determine the maximum current it may draw.

If the Sink wants to consume more than the default USB current, it shall track vRd to determine the maximum current it may draw.

6. Discover and configure optional Alternate and Accessory modes

If the Sink supports advanced functions (USB Power Delivery and/or Alternate Modes), USB PD communication through CC is required.

Entry and exit into and from an Alternate Mode is controlled by the USB PD Structured VDMs Enter Mode and Exit Mode commands through CC.

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