USB Type-C knowledge of all-round interpretation

A  USB data cable is nothing more than a line plus two heads, which seems  simple, but did not imagine the simple, small data lines, hidden many  you may not know the knowledge, and USB Type-C turned out It is not clear that it can not see it.


The  USB Type-C connector can reduce the trouble of plugging USB devices,  and USB Type-C also supports the following technologies: Data rates up  to 10Gbit / s USB3.1 specification, up to 100W power Output, audio multiplexing, and switching modes such as video signals such as DisplayPort or MHL.

Although  the industry has been dealing with USB for decades, but the realization  of Type-C connection still brings a lot of new challenges. For example, when operating at 10 Gbit / s, the voltage swing on the data line is less than 0.5V. The  designer needs to implement an equalizer in the physical layer (PHY) of  the connected receiver to obtain the input signal. In this case, the  "eye" in the eye of the signal is substantially closed and the necessary  equalization is required to In the "eyes" open, at the same time, the display signal represents the logic 0 or logic 1.

There are still many other challenges when implementing Type-C  connections, especially when the USB3.1 specification works at full data  rates of 10 Gbit / s.

USB Type-C Introduction:

1, ultra-thin

Thinner body needs thinner port, which is one of the reasons USB-C turned out. USB-C port length 0.83 cm, width 0.26 cm. The old USB port is 1.4 cm long and 0.65 cm wide. This also means that the end of the USB-C data cable will be one-third of the size of the standard USB-A data cable plug.

2, no positive and negative

Like Apple's Lightning interface, the USB-C port is the same as the front and back. That is, no matter how you insert this port is correct. Users do not have to worry about the traditional USB port brought about by the positive and negative problems.

3, fast

Theoretically, USB-C ports have a maximum transfer rate of 10Gb per second. But Apple said the new MacBook USB-C port maximum transfer rate of 5Gbps. The maximum output voltage is 20 volts, which can speed up the charging time. The USB-A type, so far the limit transfer rate of 5Gbps, the output voltage of 5 volts.

4, versatile

The new MacBook's USB-C port can transfer data, charge it as a video output port to link external display devices. The only question is how Apple meets the users who want to do these three things at the same time.

5, two-way

USB  Type-C unlike the old USB port, power can only one-way transmission,  USB-C port power transmission is two-way, which means that it can have  two transmission power mode. Therefore, users can not only use a laptop to charge mobile devices,  you can also use other devices or mobile power for the notebook to  charge.

6, backward compatible

USB-C can be compatible with older USB standards, but users need to purchase an additional adapter to complete compatibility. Apple said that not only Apple will sell the adapter, third-party companies can also authorize the production.

What are the issues that need to be addressed when developing USB Type-C?

1, reconsider PHY

For  example, the positive and negative plug-in features of the connector  need to be reconstructed in the implementation of the physical layer. When  running at USB 2.0 data rate, the designer can use a pair of resistors  to short-connect the two data paths into the physical layer to indicate  how the connector is plugged. At a lower USB 2.0 data rate, the physical layer has sufficient  performance margins to handle the reflections caused by the shorted data  path.

For USB3.0 and USB3.1 data rates, the designer needs to implement two data paths to handle higher rates. Through  a connector in the direction, the system is connected to a data path  and in the other direction the system is connected to another data path.  The dual data path is necessary because, when transmitting at 5Gbit / s  and 10Gbit / s data rates, the direction of the short pass through the  data path will cause too much signal reflection to break down the data.

The designer needs to decide how to solve the problem. One solution is to use two physical layers, each with a physical layer. The  drawback of the dual physical layer solution is that it takes 20% to  25% of the extra area to implement two SuperSpeed data paths and two  Hi-Speed data paths, and requires two sets of phase-locked loop  circuits (PLL) and two sets of power, ground and data pins. The end result is that a system-owned high-speed data path is one more than its actual needs.

A  more efficient implementation is the use of a physical layer that has  been optimized for the USB Type-C specification, which has two  SuperSpeed data paths, a Hi-Speed data path, a set of phase-locked Ring circuit and a set of power, ground and data pins.

The choice of the designer depends on their final application. The cost-sensitive market will choose to save on the area and the chip  can be achieved by eliminating an additional Hi-Speed data path and  reducing the number of pins by up to 40%.

2, USB Type-C signaling

The second challenge to implementing USB Type-C is the signal complexity required for 24-pin connectors. The  USB Type-C specification specifies the configuration channel (CC)  signal and the power output (PD) signal to define the parameters, such  as the direction of the connector, how much power can any of the wires  plugged into the Type-C port, and the connector When it is for the audio and video and in the switch mode.

While  supporting the configuration of channel signals with power output  signals required for additional logic: power output message controller  and configuration channel logic. Part of the design challenge is to deal with two signals that may  occur at different voltages, depending on the signal combination at that  time.

The Type-C specification also eliminates the USB On-The-Go concept, but instead takes the Dual Role Port concept. USB On-The-Go is a signaling method that indicates whether a port is used as a host or as a device. The  On-The-Go protocol uses the ID pin to signal whether the port is acting  as a master or a device at work; however, Type-C does not have this  signal, so it is necessary to use the power output message to do this,  which makes the PD signal To achieve further complication.

3, systemic problems

Type-C connector can make USB users more convenient life, but the cost is to make the designer's work becomes more complex. Designers will have to decide which one they want to support USB 2.0,  3.0 and / or 3.1, how to handle power output, and whether to support  audio and video switchable mode.

USB Type-C implementation will also have a system impact. For  example, if SoC intends to support power output functionality, the  designer can choose to use an external power management chip that meets  all the relevant security conditions. This means dividing the power output and configuring the channel  logic, perhaps between the physical layer and a separate power  management chip, or between the main system CPU and even a dedicated  external microcontroller.

Synopsys'  comprehensive USB controller and physical layer IP portfolio has been  successfully adopted by more than 3,000 USB designs and has been  validated with about 3 billion shipped devices. This  is an in-depth and straightforward design experience that enables us to  develop USB3.1 physical layer IP optimized for use with Type-C  connectors and support tools and verification environments necessary to  implement Type-C functionality - This makes the designer's work easier.

4, "line" of the problem

In addition to USB can be used to transfer data, but also as a means of power supply. The  initial USB standard because it does not have the power supply  capacity, so USB 1.0 and 2.0 power supply capacity is limited to 2.5w  (0.5A / 5v). Although  this is enough to supply mobile phones and other small electronic  devices, but for external drives, it is clearly not enough. And USB 3.0 came into being, its supply value of up to 4.5w (0.9a / 5v).

And  in the USB 3.1 standard USB Type-C interface power supply capacity can  reach a maximum of 20V / 5A, which is 100w, not only to meet the  requirements of mobile phone charging, but also to meet the flat-panel  equipment and computer charging needs; In addition, Power supply capacity, you can also remove other high power  consumption of external equipment need to connect another power supply  trouble.

In addition, there are some problems with USB Type-C power supply. Which is good and there are deficiencies. The good news is that the USB PD 2.0 standard can power the notebook  or tablet directly in the future, while also allowing the smartphone to  be used as a mobile power source.

On  the other hand bad news is that there is no so-called all-around USB  cable come out, these cables need to build a special chip, which  contains information on the cable. Full-featured  USB cable needs to be able to withstand 1.5a or 5v of current, and this  cable cost than ordinary USB cable much higher