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

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.

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

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

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

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 V_CONNECTOR ) 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 V_BUS 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.
• V_CONN 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.

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 (V_BUS ). A Type-C provider port corresponds to the port with R_p 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 (V_BUS ). A Type-C consumer port corresponds to the port with R_d 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 V_BUS . The DFP thus exposes R_p 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 R_d 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 R_p terminations on its CC wires when acting as a power source and exposes R_d 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

 (Source: Cypress Semiconductor)

As noted above, the USB Type-C specification describes how a Type-C upstream-facing port (UFP) applies Pull-Down resistors (R_d ) 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 (R_p ) 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 V_CONN to power the marker electronics inside the cable.  These EMCA’s expose R_a termination resistors on the V_CONN pin of the Type-C plug.  Non-Electronically Marked Type-C cables do not have electronics inside and have no need for V_CONN power.  These non-EMCA cables leave the V_CONN 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)

R_p and R_d 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 V_BUS 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 V_CONN for powering the electronics in the USB Type-C EMCA plug if an R_a termination resistor is detected.

Dual role Ports (DRP), as already discussed above, can operate as either a power Source or a Sink. A DRP exposes the R_p terminations on its CC wires when acting as the power source and exposes R_d terminations on its CC wires when acting as the power sink. DRP devices will initially toggle their state between DFP (by connecting R_p and disconnecting R_d ) and UFP (by disconnecting R_p and connecting R_d ) 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 R_p termination and the consumer, being a power sink, exposes R_d . 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 R_d termination and the power adapter, being a power source, expose R_p . 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 R_p – R_d voltage divider is formed on one of the CC lines, the connection is established.

The USB Type-C specification allows for up to 15 W to be transferred from DFP to UFP on the V_BUS 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 V_BUS voltage above 5 Vo to a maximum of 20 V and raise the V_BUS current to a maximum of 5 A. 

When operating in a “Type-C Only” environment, the voltage divider of the R_p and R_d resistors that the DFP and UFP provide respectively determines the current limit of the V_BUS power source.  The UFP must detect this R_p /R_d voltage divider voltage and use it to determine the maximum current that can be drawn from the V_BUS power source.  This R_p /R_d 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 V_BUS 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 V_BUS 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 V_BUS 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.

As described in the first part of this two-part series, 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.  In this article, we describe the USB Type-C power delivery protocol.

Figure 9 shows the PD message format. All PD messages are transmitted at 300KHz +/- 10% over the CC line.  The first 64 bits (Preamble ) are an alternating 1, 0 pattern so that the receiver can synchronize with the actual transmitted clock. The next 16-bit word (Address or Type ), contains the message address, indicating the message recipient or other type information (SOP* communication explained below). The next 16-bit field contains the message header, which is encoded as shown in Figure 9. The header field includes a data object count (#Data Objects).  If the data object count is 0, then the message type is “control.” If it is 1 through 7, then up to seven 32-bit data objects follow, and the message type is “data.” A 32-bit CRC is transmitted, followed by a 4-bit end of packet (EOP) token that completes the message. If the calculated CRC is the same as the received CRC, then the Type-C device physical layer passes the decoded message up to its protocol layer for decoding. Refer to the USB-PD specification for more details on the message structure.

Figure 9. PD message format (Source: Cypress Semiconductor)

The USB-PD specification defines two types of Messages (see Table 4):

• Control Messages are short and manage the Message flow between Port Partners or for exchanging Messages that require no additional data.
• Data Messages exchange information between a pair of Port Partners. Data messages include exposing capabilities and negotiating power, Built-In-Self-Test (BIST), and custom messaging defined by the OEM.

Table 4. PD Message Types: Control and Data (Source: Cypress Semiconductor)

Figure 10. Successful Power Negotiation. Note: Rqt – Request; Ack – Acknowledge; VDM – Vendor Defined message (Source: Cypress Semiconductor)

Figure 10 shows the message flow during a successful power negotiation between any two generic PD-enabled Type-C devices connected by an Electronically Marked Type-C cable (see Figure 11).  Note that each command and data message is acknowledged by the receiver of the message, which sends a GoodCRC response back to the initiator (not shown in Figure 10).

Figure 11. Type-C connection with EMCA (Source: Cypress Semiconductor)

• The DRP, which got locked as a DFP (Source), first discovers the presence of an EMCA attached due to the presence of Ra. It queries for the characteristics of the cable by sending the DiscoverIdentity
• The cable responds with the cable characteristics using the DiscoverIdentity ACK response message (see Figure 10).
• The DFP (Source) also detects the presence of a UFP (Sink) due to the R_d The DFP (Source) then sends the source capabilities message to the UFP (Sink) that represents the DFP (Source) power supply’s present capabilities as in Figure 10. In Figure 10, this message sends out the power supply capability as the ability to source 5 V at 3 A and 9 V at 3 A.
• The UFP (Sink) then uses a Request message for, in this case, 3 A of current at 9 V.
• The DFP (Source) sends an Accept message and then sends a PS_RDY message as an indication that the source is ready to start sourcing the new power level on V_BUS .

The UFP (Sink), on detecting V_BUS , could start enumeration if it had USB data channels.

Power Delivery communication starts with sequences of special symbols called K-code markers to delineate the start of a packet. K-codes are provided by the 4b5b line-encoding scheme used in PD communication to delineate packet boundaries.

In addition to encoding data, K-codes are used for special control functions, such as a hard reset or cable reset. The special K-code sequence signifying the start of sequence is called the Start Of Packet (SOP). Three sequences are defined: SOP, SOP’, and SOP’’. SOP* is used to refer all the three SOP sequences. Figure 12 defines and differentiates SOP* packets:

• SOP Packet : Any Power Delivery packet that starts with an SOP sequence. The communication between Port Partners (DFP and UFP) uses SOP packets. These packets are not recognized by either Cable Plug.
• SOP’ Packet: Any Power Delivery packet that starts with an SOP’ sequence used to communicate with a Cable Plug. SOP’ packets are recognized by the electronics in the Cable Plug attached to the DFP (cable plug marked SOP’ in Figure 12) and are not recognized by the other Cable Plug or the port partner in UFP.
• SOP’’ Packet: Any Power Delivery packet that starts with an SOP’’ sequence used to communicate with a Cable Plug when SOP’ packets are being used to communicate with the cable plug at the other end. SOP’’ packets are recognized only by the electronics in the Cable Plug attached to the UFP (cable plug marked SOP” in Figure 12) and are not recognized by the other Cable Plug attached to the DFP or the port partner in UFP.

Response to SOP” packets by the cable plug attached to UFP is optional, but the response to SOP’ packets by the cable plug attached to DFP is mandatory in an EMCA.  Note that the term “Cable Plug” in the SOP’/SOP’’ communication case is used to represent a logical entity in the cable that is capable of PD communication. These entities may or may not be physically located in the plug.

Figure 12. SOP* Communication (Source: Cypress Semiconductor)

SOP* communication takes place over a single wire (CC). This means that SOP* communication periods must be coordinated to prevent important communications from being blocked. Communications between the Port Partners (SOP packets) take precedence, implying that communications with the Cable Plug (SOP’/ SOP” packets) can be interrupted. See the USB PD specification for more details.

Before the USB-PD specification came into being, the USB host (such as a laptop, for example) was always the power provider and the USB device (i.e., a mouse) was always the power consumer.  Charging the battery of the host computer was considered a separate action. The PD specification greatly improves the USB ecosystem and defines power roles (V_BUS Source and Sink) that are independent of the data roles (USB host and USB device). This includes the ability to swap power and data roles independently. An example of such versatile behavior is a wall mounted peripheral device such as a monitor can charge the battery of a USB host such as a notebook or PC.

The PD specification defines three types of role swaps:

• Data Role Swap (DR_SWAP): Exchange the DFP (Host) and UFP (Device) roles between Port Partners over the USB Type-C connector. This does not swap the R_p and R_d terminations on the CC line of the port partners as the port power role remains intact.
• Power Role Swap (PR_SWAP): Exchange the Source and Sink roles between Port Partners. This also swaps the R_p and R_d terminations on the CC line of the port partners.
• V_CONN Swap (VCONN_SWAP): Exchange the VCONN (cable plug power) Source between Port Partners.

Table 5 summarizes the behaviors of a port in response to the three USB PD swap commands.

Table 5. USB PD Swapping Port Behavior Summary (Source: Cypress Semiconductor)

Figure 13 shows the message sequence during a DFP-initiated successful DR_SWAP. It can be initiated by either the DFP or the UFP. One example scenario that will need DR_SWAP for proper operation is when a USB Type-C Monitor (DRP) locks as a DFP/ Source initially when connected to a USB Type-C host (DRP).  Thus the monitor is sourcing power to the Type-C host. For proper functionality, the Type-C monitor should be UFP with the Type-C host as DFP. DR_SWAP enables the swap to be initiated by the monitor.

Figure 13. DFP initiated DR_SWAP (Source: Cypress Semiconductor)

Figure 14 shows the message sequence during a Source initiated successful PR_SWAP. It can be initiated by either the source or the sink. One example scenario that will need PR_SWAP for proper operation is when a USB Type-C Monitor (DRP) locks as a UFP/ Sink initially when connected to a USB Type-C laptop (USB host/ DRP).  In this case, the monitor initially sinks power from the Type-C host. PR_SWAP is needed to enable the monitor to charge the Type-C laptop.  This swap can be initiated either by the Type-C monitor or the laptop.

Figure 14. Source initiated PR_SWAP (Source: Cypress Semiconductor)

Figure 15 shows the message sequence during a DFP initiated successful V_CONN _SWAP. It can be initiated by either the current VCONN source or VCONN sink. As shown in the figure, both sources will be on at the same time for a short while following the Accept message. This is because the new VCONN source turns on following the Accept message and before the PS_RDY instance, and the old VCONN source turns off after the PS_RDY instance. This sequence of VCONN powering is, as per the USB-PD specification, to ensure that the cable controller always remains powered. Furthermore, to avoid the two VCONN sources being on at the same time, the specification mandates an isolation element between the two VCONN sources (e.g. a diode) to select a particular source among the two when both are available.

Figure 15. DFP initiated V_CONN _SWAP (Source: Cypress Semiconductor)

This article has provided a high level view of the basics of the USB Type-C and Power Delivery (PD) specifications. For additional information, see Type-C Essentials, Type-C Resources, and the USB Type-C and Power Delivery FAQ.

• http://www.cypress.com/video-library/Corporate/typec-101-lesson-1-intro-type-c-kits-and-tools/499096
• Specifications: Type-C Specification, USB-Power Delivery Specification
• Application notes: AN95615 – Designing USB 3.1 Type-C Cables Using EZ-PD™ CCG2, AN210403 – Hardware Design Guidelines for Dual Role Port Applications Using EZ-PD™ USB Type-C Controllers, AN210771 – Getting Started with EZ-PD™ CCG4
• Other web links: www.cypress.com/type-C, Designing a Type-C Electronically Marked Cable

Gayathri Vasudevan is a Staff applications engineer at Cypress Semiconductor, Bangalore. Gayathri is responsible for supporting customers on all wired USB products, developing specifications for next generation products, and creating solution demos, application notes and other collateral for new products. She has a degree in electronics and communication engineering.