212 lines
12 KiB
Markdown
212 lines
12 KiB
Markdown
<!-- page 21 -->
|
||
|
||
# Chapter 1. Introduction
|
||
|
||
USB Power Delivery (PD) is a power transfer standard that allows USB cables and connectors to deliver higher
|
||
power levels (up to 240W) for a wide range of devices, including laptops, tablets, smartphones, and peripherals.
|
||
In addition to power delivery, USB PD supports data protocol negotiations over USB-C, thus making it a versatile
|
||
solution for both power and data configurations.
|
||
|
||
Key features of USB PD:
|
||
|
||
- Negotiable power output – Supports negotiating power up to 240W (48V/5A) to power high-demand devices
|
||
like laptops, monitors, and gaming consoles.
|
||
- Renegotiable power – Powered devices and power sources renegotiate power levels to deliver optimal power
|
||
based on a particular Device's immediate requirements.
|
||
- Bidirectional power – Devices can both provide and consume power, enabling features like Host charging
|
||
(e.g., powering a laptop from an external monitor).
|
||
- Unified connector – Uses the USB-C connector that supports both power and data transfer through a single
|
||
cable.
|
||
- Data protocol Negotiation – USB PD allows a Device to Connect using the default USB2/USB3 data connection or switch to alternate data modes, enabling USB-C to support additional protocols such as DisplayPort,
|
||
USB4, and Thunderbolt 3 for video output and high-speed data transfer.
|
||
|
||
In summary, USB PD maximizes the potential of USB-C by providing both flexible power delivery and data protocol
|
||
negotiations, thus making it a universal solution for modern devices.
|
||
|
||
## 1.1. Cable and Connectors
|
||
|
||
The USB Power Delivery specification assumes the use of certified USB cables and associated detection mechanisms as defined in [USB-C].
|
||
|
||
## 1.2. Operational Overview
|
||
|
||
A USB PD connection is based on the underlying USB-C standard and roles as defined in [USB-C]. The Source
|
||
Port provides power, and the Sink Port consumes power. Each connection has one Source and one Sink, which
|
||
are established during the initial connection.
|
||
|
||
At the point of Attachment, the Source Port functions as both the Downstream Facing Port (DFP) and the VCONN
|
||
Source, while the Sink Port functions as the Upstream Facing Port (UFP).
|
||
|
||
Power roles (Source/Sink), data roles (DFP/UFP), and the VCONN Source role can be swapped independently
|
||
during a connection. These role swaps depend on whether the ports support Dual-Role Power (DRP) or Dual-Role
|
||
Data (DRD) Capabilities. Ports with dual-role Capabilities can switch between providing and consuming power or
|
||
acting as the data Host or Device, depending on the Negotiation.
|
||
|
||
## 1.3. USB PD Roles
|
||
|
||
### 1.3.1. Source Port
|
||
|
||
The Source Port is typically associated with devices like chargers, power banks, notebooks, and docks that power
|
||
other devices and provide the power in a USB PD connection. The Source defaults to being the DFP at initial connection. It supplies power to a Connected Sink Port and is responsible for initiating power negotiations to determine
|
||
the appropriate voltage and current levels needed by the connection.
|
||
|
||
<!-- page 22 -->
|
||
|
||
### 1.3.2. Sink Port
|
||
|
||
The Sink Port is the power-consuming Port in a USB PD connection and is typically associated with devices like
|
||
smartphones, tablets, notebooks, and peripherals that rely on an external power Source to charge. The Sink defaults
|
||
to being the UFP at initial connection. It draws power from a Connected Source Port and participates in power
|
||
Negotiation to ensure it receives the appropriate voltage and current levels.
|
||
|
||
### 1.3.3. Downstream Facing Port (DFP)
|
||
|
||
The Downstream Facing Port (DFP) is the Port in a USB-C connection associated with the USB Host role. It is the
|
||
Initiator in Data Role negotiations and handles most downstream data communications. See [USB2] and [USB3]
|
||
for more information about Downstream ports.
|
||
|
||
### 1.3.4. Upstream Facing Port (UFP)
|
||
|
||
The Upstream Facing Port (UFP) is the Port in a USB-C connection that is associated with the USB Peripheral role.
|
||
It is the Responder in Data Role Negotiation and handles most upstream data communication. See [USB2] and
|
||
[USB3] for more information about Upstream ports.
|
||
|
||
### 1.3.5. Dual-Role Power (DRP) Ports
|
||
|
||
Dual-Role Power Ports can operate as either a Source or a Sink and swap between the two Power Roles as needed.
|
||
|
||
### 1.3.6. Dual-Role Data (DRD) Ports
|
||
|
||
Dual-Role Data Ports have the ability to operate as either a DFP or a UFP and to swap between the two Data
|
||
Roles. Products can be Dual-Role Data Ports without being Dual-Role Power Ports. This means that they can switch
|
||
logically between DFP and UFP Data Roles, even if they are Source-only or Sink-only for power.
|
||
|
||
### 1.3.7. VCONN Source
|
||
|
||
The VCONN Source is the Port that provides power to Cable Plugs. The VCONN Source is typically the Downstream
|
||
Facing Port (DFP) and supplies power to enable Active Cable circuitry and support cable identification and management in USB PD connections. To commuunicate with Cable Plugs, a Port must be the VCONN Source. For more
|
||
information about a USB Type-C Source Port's requirements regarding VCONN, see [USB-C].
|
||
|
||
### 1.3.8. Cable Plugs
|
||
|
||
In the context of USB PD, Cable Plug refers to embedded USB PD communication-capable circuitry within a cable,
|
||
plug, or accessory that is typically associated with a single plug end of a cable or a captive plug on a Device. This
|
||
circuitry consists of the embedded electronic marker (e-marker) chip and/or any active circuitry within the Cable.
|
||
|
||
Cable Plugs are powered when VCONN is present but are generally not aware of the status of the Contract between
|
||
the two Connected ports. They do not initiate communication and only respond to messages that are addressed
|
||
to them.
|
||
|
||
The Source or Sink communicates with the Cable Plug circuitry to retrieve information about the Attached cable
|
||
or accessory, such as current-carrying capability or supported data rates, or to direct the plug to enter a specific
|
||
data Mode.
|
||
|
||
## 1.4. Power Delivery Operational Contracts
|
||
|
||
A PD Source and Sink will be in one of three Contracts:
|
||
|
||
<!-- page 23 -->
|
||
|
||
- Default Contract – A non-Negotiated power Contract established at the initial connection, as defined in [USBC], withadefault voltageof5V. The Sink mightdraw uptotheadvertised USB-C current. The Sourceremains
|
||
in the Default Contract until the Sink disconnects or both ports Negotiate and establish an Explicit Contract.
|
||
- Explicit Contract – The State of the Source and Sink after any PD Power Negotiation has taken place. This
|
||
is the normal operational State for PD and must be entered before other USB PD messaging can occur.
|
||
A Source offers power contracts to a Sink using USB PD messaging, and the Sink requests a Contract,
|
||
which is then accepted by the Source. Data connections and modes other than USB2 and USB3 might be
|
||
established in an Explicit Contract.
|
||
- Implicit Contract – A transitory power Contract that follows a Power Role Swap or Fast Role Swap. The
|
||
available voltage, similar to a Default Contract, is 5V, with current defined by the advertised USB-C current.
|
||
The Source in an Implicit Contract will immediately Negotiate with the Sink to establish an Explicit Contract.
|
||
All data connections and modes are maintained during an Implicit Contract.
|
||
|
||
## 1.5. Source and Sink Operation in USB PD
|
||
|
||
In a USB PD connection, the Source and Sink engage in a series of Message exchanges to Negotiate power
|
||
contracts, data roles, and Mode implementation (such as Alternate Mode or USB4 Mode). This process ensures
|
||
both ports operate with compatible power levels and functional Capabilities.
|
||
|
||
### 1.5.1. General Source-to-Sink Initial Interaction
|
||
|
||
1. Initial Connection (Attach) – Defined by [USB-C].
|
||
|
||
- The Source asserts Rp (pull-up resistor or pull-up current) on the CC line, and the Sink asserts Rd (pulldown resistor) to establish the connection.
|
||
- The Source provides a Default Contract at the advertised Rp current at 5V upon connection.
|
||
|
||
2. Power Discovery.
|
||
|
||
- The Source advertises its available power options through its Source Capabilities. These messages
|
||
define voltage (e.g., 5V, 9V, 15V, 20V) and current levels the Source can supply.
|
||
|
||
3. Power Negotiation and Explicit Contract. The Sink requests the preferred power option based on its requirements.
|
||
|
||
- The Source accepts the Request to establish the Explicit Contract.
|
||
- The Source then indicates that it is supplying the agreed power level.
|
||
- Once the Explicit Contract is established, both ports enter a stable power State and might establish a
|
||
Data Role change or Mode Entry.
|
||
|
||
4. Data Role and Mode Entry.
|
||
|
||
- When a role change is desired, the Source and Sink exchange Data Role messages to determine the
|
||
DFP (Downstream Facing Port) and UFP (Upstream Facing Port) roles.
|
||
- The Source might Request the Sink to send capability information and to confirm data Mode compatibility.
|
||
- The Source might initiate USB4 Mode Entry, if supported.
|
||
- The Source can initiate Alternate Mode Entry by asking the Sink to Advertise its supported modes.
|
||
- If a compatible Alternate Mode is found (e.g., DisplayPort), the Source requests to enter the Mode.
|
||
|
||
5. Ongoing Communication and Role Swaps
|
||
|
||
<!-- page 24 -->
|
||
|
||
- During the connection, the Source and Sink can continue to exchange Control and Data messages to
|
||
renegotiate power levels, switch roles, etc.
|
||
- Both ports can perform a Power Role Swap, where the Source becomes the Sink, and vice versa.
|
||
- A Data Role Swap can also occur, changing which Port acts as the DFP (Host) or UFP (Peripheral)
|
||
for data transfer.
|
||
|
||
## 1.6. Common PD Device Types
|
||
|
||
USB PD devices fall into a few general categories, such as:
|
||
|
||
- Dedicated power sources – wall chargers (bricks), power banks, etc.
|
||
- Host systems – computers (desktop, portable), mobile phones, tablets, etc.
|
||
- Peripherals – mice, keyboards, displays, hard drives, cameras, speakers, headsets, etc.
|
||
- Data routers – hubs, docks.
|
||
|
||
Some devices can be combinations such as a display/dock or cameras that can function as a Host or Device. With
|
||
USB PD, these can also be power Sources or power Sinks, or both, depending on what they are Attached to. For
|
||
example, a Host computer can be a power Sink and be charged when Connected to a wall Charger, but it might
|
||
then be a power Source to a downstream Peripheral such as a hard drive.
|
||
|
||
## 1.7. USB-PD Architectural Overview
|
||
|
||
This section describes the logical architecture of the USB Power Delivery (USB PD) specification. The architecture
|
||
overview presented here is conceptual and not intended to prescribe a specific implementation. Rather, it provides
|
||
a high-level framework that is referenced throughout this specification.
|
||
|
||
USB PD defines a bus protocol specifying voltage levels, current limits, Signaling, timing, and other interface parameters that are Negotiated between two ports. It does not define how these requirements must be implemented
|
||
in a particular Device. Implementation details are left to the product designer and are outside the scope of this
|
||
specification.
|
||
|
||
At a high level, USB PD is structured as a hierarchy of control layers, where each layer communicates with its
|
||
adjacent layers. From lowest to highest, these layers are:
|
||
|
||
- `Device Policy Manager`: Coordinates USB PD behavior across the Device by managing one or more ports
|
||
based on the Device's overall power and data Policy.
|
||
- `Policy Engine`: Enforces local power and data Policy for an individual Port.
|
||
- `Protocol Layer`: Constructs and interprets USB PD messages exchanged between ports.
|
||
- `Physical Layer`: Handles bit-level transmission and reception on the physical connector and performs error
|
||
detection on messages using a CRC mechanism.
|
||
- `USB-C Port Control`: Provides mechanisms to execute USB-C State machines and informing the other
|
||
layers of Attach/Detach events, plug orientation, and set and detect Type-C current advertisements.
|
||
|
||
Each Port includes its own USB-C Port Control, Physical Layer, Protocol Layer, and Policy Engine. The Device
|
||
Policy Manager is a single entity that manages all ports within the Device.
|
||
|
||
USB PD operates over a USB-C connector; as such, the State machines defined in [USB-C] reside within or closely
|
||
interact with the USB PD control layers. Similarly, voltage and current control for power delivery interface tightly with
|
||
these layers. Figure 1.1 illustrates these architectural elements.
|
||
|
||
<!-- page 25 -->
|
||
|
||
**Figure 1.1. USB PD Capable Device High Level Architecture**
|
||
|
||
|