USB Type-C and power delivery 101 – Ports and connections

USB Type-C is the newly introduced and powerful interconnect standard for USB. When paired with the new Power Delivery (PD) specification, Type-C offers enhancements to the existing USB 3.1 interconnect that lower the cost and simplify the implementation of power delivery over USB.  From a form factor perspective, the USB Type-C connector combines multiple USB connectors – Micro-B, Type-A, and Type-B – in a reversible connector measuring only 2.4 mm in height (see Figure 1).  Type-C allows developers to also combine multiple protocols in a single cable, including DisplayPort, PCIe or Thunderbolt.  Bandwidth is double that of USB 3.0, increasing to 10 Gbps with SuperSpeed+ USB3.1.  Finally, the USB Type-C connector can deliver up to 100 W.  This enables a wider range of applications to operate using USB (see Figure 2).  For more details, watch An Introduction to USB Type-C video and Type-C Basics.

In this two part series, we describe power delivery with USB Type-C, starting with ports and connectors in this article, followed by the power delivery protocol in part two.


Figure 1. USB Type-C: Connector of the Future (Source: Cypress Semiconductor)  


Figure 2. Power Delivery enables a wider range of applications (Source: Cypress Semiconductor)  

USB Type-C Protocol View

USB Type-C Signals

Figure 3 show the USB Type-C Receptacle and Plug signals. Table 1 and Table 2 summarize the list of signals used on the USB Type-C interface (receptacle and plug) as defined by USB Type-C specifications.

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Figure 3. Type-C Reversible Connections (Source: Cypress Semiconductor)  

Table 1. USB Type-C Receptacle Signals (Source: Cypress Semiconductor)

Signal Group

Signal

Description

USB 3.1

TX1p, TX1n RX1p, RX1n

TX2p, TX2n RX2p,RX2n

The SuperSpeed USB serial data interface defines a differential transmit pair and a differential receive pair.

On a USB Type-C receptacle, two sets of SuperSpeed USB signal pins are defined to enable the plug-flipping feature.

USB 2.0

Dp1, Dn1

Dp2, Dn2

The USB 2.0 serial data interface defines a differential pair. On a USB Type-C receptacle, two sets of USB 2.0 signal pins are defined to enable the plug-flipping feature.

Configuration Channel

CC1, CC2

The CC channel in the receptacle detects the signal orientation and channel configuration.

Auxiliary Signals

SBU1, SBU2

Sideband Use. SBU signals are used in the Alternate Mode supported by the Type-C specification, which enables multi-purposing of Type-C signals for alternate uses such as DisplayPort

Power

VBUS

USB cable bus power

GND

USB cable return current path

Table 2. USB Type-C Plug Signals (Source: Cypress Semiconductor)

Signal Group

Signal

Description

USB 3.1

TX1p, TX1n

RX1p, RX1n

TX2p, TX2n RX2p,RX2n

The SuperSpeed USB serial data interface defines a differential transmit pair and a differential receive pair.

On a USB Type-C receptacle, two sets of SuperSpeed USB signal pins are defined to enable the plug-flipping feature.

USB 2.0

Dp, Dn

The USB 2.0 serial data interface defines a differential pair. On a USB Type-C receptacle, two set of USB 2.0 signal pins are defined to enable the plug-flipping feature.

Configuration Channel

CC

The CC in the plug used for connection detection and interface configuration

Auxiliary Signals

SBU1, SBU2

Sideband Use. SBU signals are used in the Alternate Mode supported by the Type-C specification, which enables multi-purposing of Type-C signals for alternate uses such as DisplayPort

Power

VBUS

USB cable bus power

VCONN

Type-C cable plug power

GND

USB cable return current path

The USB Type-C Receptacle functionally delivers both USB 3.1 (TX and RX pairs) and USB 2.0 (D+ and D−) data buses, USB power (VBUS), ground (GND), Configuration Channel signals (CC1 and CC2), and two Sideband Use (SBU) signal pins.

To enable Type-C cables to be reversible, the Type-C receptacle is fully symmetrical. All power, ground, and signal pins are duplicated about the symmetry axis, which allows the Type-C plug to be flipped with respect to the Type-C receptacle. The Type-C plug offers only one CC pin, which is connected to one of the CC pins of the Type-C receptacle, to establish the Type-C orientation. The other CC pin is repurposed as VCONN (abbreviation for VCONNECTOR ) for powering the electronics in the USB Type-C plug.

When the Type-C plug is rotated (as shown in Figure 3):

  • GND, USB 2.0 and VBUS signals maintain connection. USB 2.0 signals are repeated in the top and bottom rows of the Type-C receptacle to maintain connectivity in either orientation.

  • VCONN or CC pin on the plug may be connected to either of the configuration channel pins – CC1 or CC2 of the receptacle – depending upon the orientation.

  • One of the two Superspeed lanes maintains the right connection, which must be appropriately routed at the receptacle side using a SuperSpeed mux.

USB Type-C ports

The USB Type-C and Power Delivery specifications have defined different types of USB Type-C ports, based on the flow of data in a USB connection (i.e., data role of the port) and the direction of power in a PD connection (i.e., power role of the port).

The ports based on a data role are:

  • Downstream Facing Port (DFP): typically the USB Type-C port on a host, such as a PC or downstream port of a hub, to which devices are connected.

  • Upstream Facing Port (UFP): The USB Type-C port on a device (i.e., US Flash Drive, USB Monitor, USB mouse) or upstream port of a hub that connects to a USB host.

The ports based on a power role are:

  • Provider/Source: This is a USB port capable of providing power over the power conductor (VBUS ). A Type-C provider port corresponds to the port with Rp terminations (pull-up) asserted on its CC wires (CC1 and CC2).

  • Consumer/ Sink: This is a USB port capable of sinking power from the power conductor (VBUS ). A Type-C consumer port corresponds to the port with Rd terminations (pull-down) asserted on its CC wires (CC1 and CC2).

In its initial (default) state, the DFP is the power source and thus sources VBUS . The DFP thus exposes Rp terminations on its CC wires by default. In its initial (default) state, the UFP is the power sink and thus sinks VBUS. The UFP thus exposes Rd terminations on its CC wires (see Figure 4).


Figure 4. Default Terminations on CC pins for DFP/ UFP.  Shown here is the case when a UFP with Type-C plug (e.g. a Type-C dongle or USB Flash drive) is connected to a DFP with Type-C receptacle (e.g. a laptop) (Source: Cypress Semiconductor)

The Type-C and Power delivery specification also define a Dual Role Port (DRP) that can operate as either a Source or a Sink. The power role of the port can be reversed dynamically. A DRP exposes the Rp terminations on its CC wires when acting as a power source and exposes Rd terminations on its CC wires when acting as a power sink (see Figure 5).


Figure 5. Terminations on CC pins for DRP (Source: Cypress Semiconductor)

A typical DRP device can perform the roles listed in Table 3.  PD-enabled USB products such as notebooks with a Type-C port can generally operate as DRPs.

Table 3. Roles of DRP Device

No.

Port Data Role

Port Power Role

CC Terminations

1

DFP

Source (Power Provider)

Connect Rp and disconnect Rd

2

DFP

Sink (Power Consumer)

Disconnect Rp and connect Rd

3

UFP

Source (Power Provider)

Connect Rp and disconnect Rd

4

UFP

Sink (Power Consumer)

Disconnect Rp and connect Rd

 (Source: Cypress Semiconductor)

Detecting the Type-C connection and orientation

As noted above, the USB Type-C specification describes how a Type-C upstream-facing port (UFP) applies Pull-Down resistors (Rd ) on Configuration Channel pins CC1 and CC2 to signify that it is a device and the Type-C downstream-facing port (DFP) is required to have Pull-Up resistors (Rp ) on CC1 and CC2.  The resulting resistor divider is used to determine the Type-C device attach and detach. The orientation of the Type-C cable plugs in each receptacle is easily determined as only one of two CC pins is connected across the cable (see Figure 6).

Type-C Electronically Marked Cable Assemblies (EMCA) are cables that require VCONN to power the marker electronics inside the cable.  These EMCA’s expose Ra termination resistors on the VCONN pin of the Type-C plug.  Non-Electronically Marked Type-C cables do not have electronics inside and have no need for VCONN power.  These non-EMCA cables leave the VCONN pin floating on the Type-C plug.  For more details on implementing EMCA, see Designing a Type-C Electronically Marked Cable and Designing USB 3.1 Type-C Cables.


Figure 6. Type-C Connection/ Orientation Detection (Source: Cypress Semiconductor)

Rp and Rd termination resistors on the Type-C receptacle CC pins make it possible to detect the connection event and identify the orientation of the Type-C plugs in the receptacles. The DFP and UFP monitor both CC pins on the Type-C receptacle for a voltage change from their unterminated voltages to detect the connection event. The UFP also monitors for VBUS as a second indicator of a DFP connection. Both DFP’s and UFP’s can determine the Type-C cable plug orientation on their respective ends of the connection.  This is possible because only one of the CC pins is connected through the cable. After the connection and orientation is detected, the other CC pin is repurposed by the DFP as VCONN for powering the electronics in the USB Type-C EMCA plug if an Ra termination resistor is detected.

Connecting two Type-C Dual Role Ports

Dual role Ports (DRP), as already discussed above, can operate as either a power Source or a Sink. A DRP exposes the Rp terminations on its CC wires when acting as the power source and exposes Rd terminations on its CC wires when acting as the power sink. DRP devices will initially toggle their state between DFP (by connecting Rp and disconnecting Rd ) and UFP (by disconnecting Rp and connecting Rd ) operation, until the complimentary termination is found at the port partner on one of the CC lines, for a successful Type-C connection detection as depicted in Figure 7.


Figure 7. Type-C connection between two DRPs (Source: Cypress Semiconductor)

When a DRP device (e.g. PC) is connected to a power consumer (e.g. a mouse), a successful Type-C connection occurs when the DRP device (e.g. PC) exposes the Rp termination and the consumer, being a power sink, exposes Rd . Thus, the DRP port of the PC locks as a DFP (initially) in this case.

On the other hand, when a DRP device (e.g. PC) is connected to a power provider (e.g. a power adapter), a successful Type-C connection happens when the DRP device (e.g. PC) exposes Rd termination and the power adapter, being a power source, expose Rp . Thus the PC port locks as a UFP (initially) in this case.

When two DRPs are connected together, they accept the resulting DFP-to-UFP relationship achieved randomly. Both DRPs toggle their states between DFP and UFP as depicted in Figure 7. Whenever a successful Rp – Rd voltage divider is formed on one of the CC lines, the connection is established.

USB Power Delivery (PD) Protocol View

The USB Type-C specification allows for up to 15 W to be transferred from DFP to UFP on the VBUS and Ground signals.  This 15 W can only be transmitted at 5 V when a “Type-C Only” device is used.  Adding USB Power Delivery to a “Type-C Only” device makes a “Type-C PD” device which can raise the VBUS voltage above 5 Vo to a maximum of 20 V and raise the VBUS current to a maximum of 5 A. 

When operating in a “Type-C Only” environment, the voltage divider of the Rp and Rd resistors that the DFP and UFP provide respectively determines the current limit of the VBUS power source.  The UFP must detect this Rp /Rd voltage divider voltage and use it to determine the maximum current that can be drawn from the VBUS power source.  This Rp /Rd voltage divider voltage is not static as the DFP can dynamically change its current limit as environmental variables of the charging ecosystem change.  The UFP must always monitor this voltage and obey the new VBUS current limit that is dictated by the DFP.

This behavior of a “Type-C Only” device where the DFP dictates and a UFP obeys illustrates one weakness of the “Type-C Only” approach.  Negotiation does not exist in a “Type-C Only” approach where a Type-C PD device has bidirectional negotiation of VBUS voltage and current levels.  By adding USB-PD to a “Type-C Only” device and creating a “Type-C PD” device, you can achieve the necessary flexibility of VBUS power negotiation.

When USB PD is implemented, USB PD Bi-phase Mark Coded (BMC) carried on the CC wire is used for USB PD communications between USB Type-C ports.  Figure 8 illustrates how the USB PD controller connects to the CC wire and introduces BMC signaling to the USB Type-C cable’s CC wire. In the figure, only one of the CC lines (that which is connected through the cable) is shown.


Figure 8. USB Power Delivery over Type-C (Source: Cypress Semiconductor)

An explicit power contract or agreement is reached between a Port Pair as a result of the Power Delivery negotiation process. The power delivery negotiation happens using PD Messages (defined by the USB-PD specification) over the CC wire in a Type-C connection.

In part two, we describe details of the power delivery protocol.

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