USB-C – a new version of the well-known wired communication interface

USB-C – one of the most popular standards for wire communication in electronics

After Ethernet, USB is the most popular standard for wired communication in consumer and professional electronics. It has been present on the market for over 20 years. Thanks to improvements of its successive versions, this interface has become ubiquitous – most consumer electronic devices are manufactured with this connector. The new version of the USB Type-C connector, which debuted on the market in 2014, in combination with the USB 3.1 specification, brings many improvements and noteworthy novelties.

The most visible is the change in the design of the plug and socket. The dimensions of the 24-pin Type-C plug resemble a Micro-B plug (8.4 × 2.6 mm). Its hallmarks are rounded corners and a hollow center. This distinguishes it from the USB Micro-B plug, which has cut corners. Dimensions are an important aspect here from the point of view of device designers, as smaller and thinner sockets facilitate the design of flat housings.

The convenience of using the Type-C plug is primarily ensured by the freedom to insert it into the socket. This reduces the time it takes to connect, for example, peripheral devices to the computer. As a result, the durability of the joints should also be significantly extended. It is assumed that it must withstand at least 10 000 cycles of joining.

Its universality is believed to be the main component of the potential of the USB Type-C interface and the USB 3.1 specification. This feature is ensured by two specifications: Alternate Mode and Power Delivery (PD). Thanks to the first, the port can send audio and video data for transmission, which were previously used, among others DisplayPort, HDMI, Mobile High-Definition Link and Thunderbolt. There are five device charging profiles in Power Delivery. They will allow power consumption in the range from 10 (5V, 2A) up to 100W (20V, 5A).

It is worth noting that the mentioned power levels are ensured with simultaneous data transmission. Previous generations of USB provided much lower ratings or required the use of cables and connectors for power only. The Type-C connector is the same on both sides of the cable, and the plug is additionally reversible, therefore the entire system includes the Configuration Channel (CC) functionality, which is responsible for detecting the functions of the receiver attached to the host and recognizing its technical capabilities in the field of communication, voltages and currents. In addition, the CC determines which pairs of wires will transmit and what polarity they will have (D + changes with D- by rotating the plugs, etc.). This solution ensures great versatility of the new version of the interface, but also the requirements for electronics designers are clearly greater. Probably for these reasons, companies investing in the development of products for USB-C have created the USB Implementers Forum (USB IF) group, which cares about the compliance and technical level of solutions, and its members exchange experiences. The USB IF includes, among others STMicroelectronics.

The high power supply that the USB-C port can deliver to the receiver places great technical demands on the quality of the cables. The same applies to fast transfer, which can only be achieved if the cable is of high quality: screened, symmetrical and of equal performance along the entire length. Therefore, cables capable of delivering a current greater than 3 A or of high-speed transmission are marked by placing an E-marker chip inside the housing informing the host about the limits.


USB Type C vs previous versions of this interface

WTable 1 summarizes the most important differences between USB Type C and previous versions of this interface.

Table 1. USB Type C and previous versions of this interface
Power supply

USB 1.x/2.0

1 = VBUS, 4 = GND
3 = Data+, 2 = Data-
USB 1.0 / 1.1
small speed 1,5 Mbps
high speed 12 Mbps
USB 2.0
high speed 480 Mbp
5 V / 500 mA
5 V / 1,5 A
(for charging systems)

USB 1.x / 2.0 Mini

1 = VBUS, 5 = GND
3 = Data+, 2 = Data-
4 = ID pin: host = GND, device = without connection

USB 1.x / 2.0 Micro

1 = VBUS, 5 = GND
3 = Data+, 2 = Data-
4 = ID pin: host = GND, device = without connection

USB 3.0

1 = VBUS, 5, 8 = GND
2 = Data-, 3 = Data+
4 = USB-OTG,
6 = Tx-, 7 = Tx+, 9 = Rx-, 10 = Rx+
USB 3.0
Super speed
5 Gbps
5 V / 900 mA

USB Type-C:
Smaller physical size
Reversible plug
Greater voltage and current
Automatic configuration
The highest transfer


Data-, Data+ for backwards compatibility
Two pairs of RX1/2 and TX1/2
CC1/2 for configuration
VCONN (to power the cable ID chip)
SBU 1/2 for audio transmission
USB 2.0
high speed: 480 Mbps
USB 3.0
Super speed: 5 Gbps
USB 3.1
Super speed+: 10 Gbps
By default 5 V / 1,5 A
5 V / 3 A max.
From 5 to 20 V, 5 A max.
USB PD 3.0 z PPS
From 3 to 20 V, 5 A max.


Powering and charging devices with USB Type-C

Looking at the figure below, it is not difficult to notice that ensuring the ability to rotate the plug in the socket in the USB Type-C version requires switching the signal lines. The ones responsible for the lower speed and compatibility with the old USB versions (Data + and Data-) are placed exactly in the center of the connector and additionally they have been doubled and inverted in the bottom row of the socket. Thanks to this procedure, no matter how the plug is inserted into the socket, it will always ensure their correct connection. The TX and RX lines responsible for high speed communication, on the other hand, cannot be so connected and therefore there is an additional CC signal line to detect the cable orientation and switch the TX / RX signal lines in the controller accordingly to match.

The layout of the pins in the plug and USB Type-C socket

Another difference between the old and the new USB is the symmetry of the cable. The new standard uses an identical plug on both ends, which means that determining who in transmission is the host and who is the receiver (device) is not imposed in advance and requires agreement using the protocol. Moreover, this arrangement concerns not only data transmission, but also the direction of transmission of the power supply.

For data transmission, the host is now called Downstream Facing Port (DFP) and the receiving device is Upstream Facing Port (UFP). For power transmission, the power supplier is Source and the load is Sink. In some applications, when a given equipment can power and also be powered, we talk about dual functionality – Dual Role for Power (DRP). It is also intended for data transmission – Dual Role for Data (DRD). Determining the role played by a given device is determined by the exchange of information between the controllers on both sides using the CC (Configuration Channel) control line.

The big change and difference between USB-C and older versions of the interface are the power supply options. The first versions of USB delivered only 2.5 W, the latest solution is able to deliver from 15 W (5 V / 3 A) to even 100 W (20 V / 5 A). This opens up the possibility of USB powering of much more complex equipment, such as monitors, as well as fast charging of mobile devices with high current. USB-C also allows you to program the parameters of the supply voltage – the Programmable Power Supply (PPS) function – in order to compensate for voltage drops on the cables by precise voltage regulation or to ensure energy savings. In this way, it is also possible to effectively charge the lithium-ion battery without the need for additional power conversion, because it is possible to reduce the value of the supply voltage VBUS to even 3 V.


Configuration of data transmission and power supply in USB-C

Rys. Proste połączenie przewodowe bez odwróconej wtyczki

The picture shows a USB connection with a non-inverted cable and without an inverted plug. From the left to the right socket, the RX1 line connects to TX1 and RX2 to TX2. Likewise, D + connects to D- from D- to D-, SBU1 to SBU2. Pin CC1 connects via the CC line on the cable to CC1 on the other side.
USB 3.1 uses only two pairs of cables for transmission, hence in this case high-speed data transmission is achieved by connecting RX1 ± and TX1 ± from one side to the other.
It is also important that VCONN does not connect both sides. This voltage is needed to power the E-mark chip and is supplied by the device at one end or the other only after it has been determined that the cable has the chip mounted.

Connection for a crossover cable with a non-rotated plug

The following figure shows a schematic of a USB connection with the cable twisted (90º) and the plug straight. In this case, looking from left to right, RX1 connects to TX2 and RX2 to TX1. The D + line is connected to D + and D- from D-, SBU1 to SBU1 and SBU2 to SBU2. Likewise, CC1 connects to CC2 via the CC line. High speed data transfer must be from RX1 ± and TX1 ± on the left to RX2 ± and TX2 ± on the right. This means that the communication transceiver contained in the controller must switch to other pairs. There are 4 connection options in total: with or without a rotated plug, and with or without a crossover cable. In systems compatible with USB 3.1, the RX / TX data lines must therefore be able to be over-voltage in the internal multiplexer in order to ensure correct communication. The possible directions of communication within the USB-C ports are shown in Fig. 11. The orientation of the plug and cable is detected on each side by the CC and CC1 pins, and then the CC (Channel Configuration) logic controller positions the input multiplexers so that the communication lines provide the correct data flow regardless of the type of cable used and the position of the plug.

Possible communication directions within the USB-C ports

Power transmission

Picture illustrates the basic USB-C power supply in the simplest setup where power is only transmitted in one direction from Source to Sink.

Basic power supply using USB-C

The power supply system includes a MOSFET transistor connected in series with the VBUS, operating as a switch that enables or disables the power supply. As a rule, it works together with a current sensor in the form of a series measuring resistor in order to protect the VBUS power bus against short circuits and overloads and to perform the potential discharge function. Both parts of the circuit have CC1 and CC2 inputs, which are connected via plugs and a cable, providing the ability to communicate to determine the required power level, voltages and maximum current values.
At the beginning, the VBUS bus is not powered, because it is not yet known what the configuration of the system is and what the receiver requirements will be. To establish this, the source of the power supply (Source) pulls the CC lines on its side, and the receiver (Sink) on the other side pulls these lines to ground.

The method of determining the USB-C role played by the individual components of the role in the power system, cable orientation, as well as the maximum current efficiency

First, the power source pulls the lines CC1 and CC2 to power through the resistor Rp and then monitors their condition. When it is high, it means that nothing has been connected yet. When the receiver is connected, the potential of the CC1 and CC2 lines decreases as the voltage is pulled towards the ground by means of the Rd resistors in the receiver. Since there is only one CC line in the cables depending on the position of the plug, either one or the other lowers its potential.
Secondly, the receiver also checks the state of the CC1 and CC2 lines to see if the voltage has increased. This state means that the power source has been connected to the system. The voltage level that will be set on the CC line after connection informs the receiver how much power the energy source has.
In practical implementations, pull-up resistors are most often replaced by current sources, due to the greater simplicity of circuit implementation in the integrated structure and because the sensitivity of such a circuit to voltage fluctuations is thus reduced.
The standard states that Rd should have a value of 5.1 kΩ on the receiver side. Therefore, the voltage on the CC line is determined by the values ​​of Rp (or the efficiency of the current source) in the Source part. It was assumed that these levels will be three: the lowest voltage on the CC line (about 0.41 V) is the default USB power value (thus 500 mA for USB 2.0 or 900 mA for USB 3.0). For the higher value (about 0.92 V), the current efficiency was set at 1.5 A. When the voltage reaches 1.68 V, the maximum current may reach 3 A (Table 2).

Table 2. Values of Rp and Rd resistors and current source efficiency for USB-C
Energy source operating mode
Current source efficiency at the source for 1.7-5.5V
Pull-up resistor for 4.75-5.5V
Pull-up resistor for 3.3 V ± 5%
Default power
80 µA ±20%
56 kΩ ±20%
36 kΩ ±20%
1,5 A @ 5 V
180 µA ±8%
22 kΩ ±5%
12 kΩ ±6%
3 A @ 5 V
330 µA ±8%
10 kΩ ±5%
4,7 kΩ ±5%

The picture shows an oscillogram showing the voltage waveforms on the interface lines during the connection of the power source to the receiver using a standard USB Type-C cable.

The moment of connecting the USB-C cable to the socket

Initially, the lines CC1 and CC2 in the power source are pulled up by the resistors Rp and CC1 and CC2 on the receiver side are pulled to ground by the resistances Rd. When the wire is connected, the voltage on one of the CC1 or CC2 lines increases depending on its orientation. In the case shown, the wire is not inverted, hence CC1 at the source links CC1 at the receiver and the voltage across it increases depending on the Rp / Rd ratio. The receiver measures this voltage and thus determines how much current it is able to take from the source. In the example shown, the voltage on the CC1 line is 1.65 V, which means that the source is capable of delivering 3 A.
After completing this process, the voltage of 5 V on the VBUS is switched on. In the simplified version of USB-C without the support of the PD power profile, the Rp / Rd divider also sets the maximum value of the current, but the source is only able to supply 5V. In the PD version, the VBUS voltage can be increased from 5V to even 20V. what the value is to be determined between the source and the receiver using the serial BMC protocol running on the CC line.
A schematic diagram of the USB-C power supply system with Power Delivery support is shown on the picture.

Diagram of the power supply system in USB-C with support for power profiles (PD)

The source in this case includes a voltage stabilizer controlled by a controller. Depending on the value of the input voltage and the required VBUS voltage, the stabilizer can be a buck converter, boost converter, buck-boost or flyback converter. Communication via the CC line is supervised by the PD controller, and the same applies to the VCONN voltage to the CC line for the needs of the E-mark system.
After communication is established, the devices supporting the PD function begin SOP communication over the active CC line to establish a proper power profile. The receiver polls the source for the availability of individual profiles (VBUS voltages and currents). Since the receiver-side controller is usually part of a larger whole and the system, it is usually the microcontroller that controls the operation of the receiver (e.g. a charger) that communicates via I2C with the receiver’s PD controller to establish power requirements.
Figure 16 shows that the PD receiver handles the request to set a higher VBUS voltage value.

The process of increasing the VBUS voltage in a system supporting PD

Communication via the CC line in this case is as follows:
• The receiver sends a request to the source to provide the available capacity.
• The source sends information about the available performance.
• The receiver selects the desired power profile from the list and requests the source to set it.
• The source accepts the request and sets the VBUS potential. During this time, the receiver minimizes the load on the VBUS so as not to disturb the state change. The voltage is set smoothly with a given rate of change.
• After setting the bus voltage value, the source waits a while for the VBUS potential to stabilize, then sends a Power Supply Ready signal to the receiver. From this point on, the receiver increases the VBUS load to the set value.
When there is a need to lower the power shaft potential, the change process is carried out in the same way, except that the source activates the capacitance discharge circuit connected to the VBUS to accelerate the change process.
This method of determining the power conditions ensures that the system will work stably and within the range of available possibilities each time. When the USB cable is disconnected, the power bus voltage is disconnected, and each subsequent operation starts with the lowest value available (5V). This prevents possible damage.
Communication uses BMC (Biphase Mark Code) coding. It is a protocol using one line for data exchange, where logic 1 is transmitted on the 1- & gt; 0 edge, and logical zero as a constant 1 or 0. Each data packet consists of a preamble with the sequence 0-1-0, the beginning of the packet SOP (Start Of Packet), header, communication data bytes, checksum CRC and EOP (End Of Packet).

Biphase Mark Code Coding Scheme

It illustrates the information exchange process after sending a VBUS boost request. The enlarged section is the preamble.

Communication when increasing the VBUS voltage

BMC data can be decoded with specialized software. A tool such as the Ellisys EX350 Analyzer allows you to capture the entire frame and further analyze individual parameters and time dependencies.

Decoded BMC data

USB-C power profiles

The USB Type-C PD 3.0 specification defines the following power profiles – Power Delivery.

USB-C power profiles

The VBUS voltage can be set to one of 4 levels: 5, 9, 15 and 20V. For the first three values, the maximum current is 3A. For 20V, the maximum current for a standard cable is 3A (60W), but for the cable with an integrated E-marker chip, this increases to 5 A (100 W).

Cables with E-marker chip

The USB-C standard allows the use of various types of cables. For low transmission speeds, you can use those from USB 2.0. There are no special requirements, except that the conductor cross-section must allow a current of up to 3 A. Cables for high-speed data transmission or for higher loads must have an identification chip built into the plug. Such a cable is called active and, apart from the E-marker circuit, it may also contain a driver that provides additional signal conditioning. Fig. 21 shows what this solution looks like from the layout side. As you can see, the power source is the VCONN pin.

Connecting the E-marker chip

Cables with a chip have internal Ra 1 kΩ resistors pulling the VCONN lines to ground, so with a value lower than Rd (5.1 kΩ). Thus, when the active cable is inserted into the socket, the voltage on both CC1 and CC2 lines will drop, however, since Rp ≠ Rd this drop will not be the same for each line, which allows the orientation of the wire to be detected. At the same time, the connection signals to the source controller that a 5 V supply on the VCONN necessary to power the E-marker chip is required.
Picture shows the voltage waveforms when a load is connected to the power source via an active cable. After powering up the E-marker chip, data is exchanged between the controller in the power source and the E-marker, and then between the source and receiver (SOP).

The process of connecting the cable with the E-mark chip

Receiver and source in one device

When the device can act as both an energy source and a receiver, this functionality is called Dual Role for Power (DRP). In this case, before the connection is made, such devices switch pins CC1 and CC2 from high to low state. When they are on both sides, this action occurs at both ends.

Process of establishing power roles in DRP

In the case shown in the figure, the left DRP acts as the source and the right one is the receiver. But it can be the other way around and what’s more, the role played by the equipment can change after connection. Each of the DRP devices can request a Power Role Swap at any time.

Swap power roles under DRP

One plug to rule them all

With the recent introduction of the USB-C connector standard supporting up to 100W of power, universal charging has become a reality for users, especially the younger generation, who are looking for greater mobility and versatility, and also care about the environmental impact.

Today, more and more devices and applications include USB Type-C connectors. Here are the reasons:

  • Thanks to the reversible plugs, you can connect it to the device in any way. The plug always fits, regardless of whether you turn it down or up
  • USB-C can transfer up to 100 W of charging power (from 5V / 0.5A to 20V / 5.0A);
  • It can combine both older functions of USB type A and B connectors in one port

usb-c STUSB4500L controller

STUSB4500L, USB Type-C controller for sink devices

Why USB-C solution is worth implementing?

For devices with a power requirement of up to 100 W (e.g. 20V 5A), the new USB standard offers a charging connector alternative to any input plug (e.g. USB micro-B or standard DC). The main advantages are:

  • Smarter design: Due to its thickness and robustness, the C-type connector makes the product shape more “smart” than in the case of the older DC type.
  • Versatile: In most cases, USB-C makes the device compatible with universal AC adapters.
  • Savings: : Retailers no longer need to include a dedicated AC adapter for each device in the box.
  • Convenience: Users do not need to carry multiple AC adapters with them when traveling. One cable works for all.
  • Nature-friendly: generates less electronic waste.

po co wdrażać usb c

Advantages of using USB-C

Global change to applications with USB Type-C solution

The first market that adopted USB-C solutions on a large scale was, of course, the market of smartphones and laptops. At present, virtually all newly manufactured smartphones and laptops have a USB-C connector. Thus, USB has also appeared quickly in the AC adapters and power banks. But it is not everything.

The changes in electronic standards were followed by the automotive market (update from STD-A or 12 V plugs from the cigarette lighter socket to USB Type-C with Power Delivery), the market for displays (ultra-thin modules), headphones (fast charging) and consumer electronics and industrial devices based on battery power.

aplikacje usb c

Exemplary applications with USB-C

How can I migrate from micro-B to USB-C?

STMicroelectronics provides designers with a comprehensive solution that helps them migrate applications from USB Type Micro-B ports to Type C ports based on a standalone USB Type-C port controller: STUSB4500L.

STUSB4500L is a USB Type-C controller that supports sink devices. This device supports dead battery mode and is suited for sink devices powered from dead battery state. It is able to operate without any external software support for quick application power-on and immediate charging process start. At type-C connection, the STUSB4500L seeks CC pin for SOURCE termination and monitors VBUS voltage in order to protect the application from an incorrect SOURCE operation.

migracja do usb c

SINK devices: Why we recommend type C controller?

From the hardware side, the evaluation board for STUSB4500 – EVAL-SCS002V1 will help in designing. It can be used as a small reference project to quickly migrate any USB mini-B, micro-B or STD-B application to USB-C. Schemes and source code samples are also available. For more information, please contact

migracja do usb c

STUSB45 controller for USB-C

How can I migrate from a custom power plug or DC connector to USB-C?

If you are planning a project to modernize the application by replacing the dedicated plug with the universal USB-C, it is worth using an independent USB PD STUSB4500 controller for SINK devices. The STUSB4500 chip is small, secure, certified and easily configurable. It can be powered from VBUS only, so it does not draw local electricity. This solution preserves the battery life. The EVAL-SCS001V1 evaluation board provides fast and easy migration from DC to Type C ports. Diagrams and source code samples can also be downloaded. For more information, please contact .

migracja do usb c

USB-C – STMicroelectronics solutions

New STMicroelectronics Products for New USB-C Applications

In addition to conforming to USB I/F requirements, application specific functions are required. The aim is to ensure safe work and to maintain an adequate level of protection regardless of the use case.

As each USB Type-C implementation is different and application-specific, STMicroelectronics offers several reference designs. Thanks to these examples, you can reduce the time and cost while developing your own project.

USB Type-C and USB Power Delivery – solution description

The AEKD-USBTYPEC1 demo kit allows for the evaluation of the USB Power Delivery protocol stack version 2.0 implemented on the ASIL-B automotive grade 32-bit Power Architecture® microcontroller.

The kit is composed of the following boards: SPC58 MCU board with CAN, LIN, Ethernet among others and an interface board hosting two USB Type-C controllers (STUSB1702) for two separate ports. On top of the interface board, a specific connector is provided for external power boards able to extend available power profiles (PDOs). Together with this, an easily customizable software is provided: the software runs parallel tasks on a free real-time operating system (RTOS).

usb c

USB-C – STMicroelectronics solutions