How to solve various problems in the development of USB Type-C applications

The latest USB Type-C is faster, has better power transfer performance, and supports a variety of video and audio transfer protocols. However, due to the more complex functions and uses, application developers have to consider more details when integrating the USB Type-C interface. Making good use of the reference design can effectively solve the difficult problems encountered in the application development process.

The latest USB Type-C is faster, has better power transfer performance, and supports a variety of video and audio transfer protocols. However, due to the more complex functions and uses, application developers have to consider more details when integrating the USB Type-C interface. Making good use of the reference design can effectively solve the difficult problems encountered in the application development process.

Most common Electronic devices are equipped with some type of Universal Serial Bus (USB) port. Such ports include Micro, Mini, and Type-A, and all of them can be used in 2.0 or the newer 3.1. Compared to these ports, USB Type-C is a huge leap forward in functionality, with faster speeds and better power transfer performance. With this more advanced connector, all the problems of its predecessor can be solved. Type-C handles high-speed data, video, and a lot of power. With these expansion functions of Type-C, consumers only need to use Type-C cables to charge, stream video or transfer data, without having to use various cables. u Manufacturers basically only need to provide and develop Type-C ports in their devices to support different uses.

Supports multi-protocol Type-C to improve device usability

The versatility of Type-C complicates designs as the extremely simple inner workings of USB are now replaced by more complex embedded components when using cables, ports, Dongles, and hubs. The seemingly simple HDMI to Type-C cable is not easy to design, because it requires embedded devices. Two major challenges arise when developing a Type-C solution. The first is dealing with the wide range of power that the port can provide. The second is to avoid communication failures that may occur due to the increase in supported communication standards. When two devices are connected, the Power Delivery (PD) protocol begins to execute.

The procedure requires negotiation between the power delivered, the power supply and the power consuming device. Since this communication needs to detect, read, and process analog and digital signals, MCU functions need to be accessed through host ports, cables, or embedded MCUs in Dongles. A failure occurs when a device or host cannot support each other and cannot establish communication. After the signal is detected, the signal will be transmitted to the host, and further MCU functions are required.

USB Type-C can not only reduce the number of cables used, but also ensure smooth cooperation between devices, bringing considerable convenience to the lives of users and consumers, but also causing trouble for designers and developers . At present, there are many types of USB ports and cables on the market, including Mini, Micro, Type-A, Type-B, etc. There are so many types that it is easy to get confused. For example, a mobile phone has a different port than a laptop, and a laptop has a different port than a digital camera. USB Type-C reduces most of the connections to a single standard (Figure 1), covering all devices and improving usability. USB Type-C supports multiple protocols and is backward compatible with USB 2.0. Nearly all accessories such as monitors, headphones, chargers, and keyboards can use USB Type-C to communicate with devices such as computers, tablets, and smartphones.
 

How to solve various problems in the development of USB Type-C applications

The configuration of connecting ports and connecting lines is shown in Figure 2 and Figure 3. Due to the signals in the socket port, the USB 3.1 SuperSpeed ​​TX/RX, VBUS, GND and all other pins will be connected correctly regardless of the directionality. From the user’s point of view, because the Type-C cable can be inserted in either direction, it is an upgraded version of the Type-A port.

How to solve various problems in the development of USB Type-C applications

USB Type-C is versatile and easy to use, but it adds to the internal complexity of a USB Type-C device. While the increased power capacity can provide up to 100W of power to charge high current devices, it also creates problems for devices that do not require such high power. The power transmission agreement also came into being. PD ensures that the proper range of power is delivered or available through any connected device.

The host downlink/device uplink ports must agree on the power

Before discussing USB Type-C, it is necessary to distinguish between device, host, power supply (power source) and power sink (consumer). A host is not necessarily a power source, so the two terms cannot be used interchangeably. The host initiates all communications and the device responds. Generally speaking, the host is the downstream port (or DFP); the device is the upstream port (or UFP). If two hosts are connected, the host can act as a dual-purpose port (or DRP), switching between host and device roles. The following example provides an illustration for the above words: When connecting a keyboard to a laptop, the keyboard is the UFP and consumer, and the laptop is the DFP and power supply.

The initial power transfer protocol between connected devices is performed through a series of resistors that act as voltage dividers on the CC line when the Type-C plug is inserted into the socket. Since the CC line in the plug connects to either CC1 or CC2 in the receptacle, the receptacle can determine the orientation of the plug simply by measuring the voltage on the CC1 and CC2 lines. The different values ​​of the pull-up resistors communicate the amount of current that the power supply can supply and determine what UFP and DFP are. There is no way for a power consuming device to indicate the amount of current it consumes through different pull-down resistor values, but must constantly adjust its load to match the maximum current the power supply can supply.

To be able to read the voltage divider correctly, both devices require an analog processing unit, usually in the form of a sophisticated ADC inside the MCU. The ADC continuously measures the voltage on the CC line, thereby monitoring the connection between the plug and socket. The MCU, also known as the PD controller, handles the complete physical layer as well as upper layer protocols, and also negotiates the power being transmitted or received. For simple Type-C applications, the power negotiation mechanism can be stopped using resistors. But in order to provide a more adaptable design, devices can agree on different settings by communicating on the CC line.

After determining the plug orientation and initial power, the devices communicate with each other using the CC line (Figure 4). In this way, devices can agree on different power sources and assign consumers or sources to adjust power delivery on the fly. CC line communication can also be used to inform the type of communication to be used. As mentioned earlier, USB Type-C can communicate over high-speed lines, USB 2.0, etc. The device will notify which of these lines is available through the CC line. But not all devices support all protocols.

How to solve various problems in the development of USB Type-C applications

If the two connecting devices do not support each other, a failure will occur. For example, if a monitor that can only receive video from the host is connected to a host that cannot support or provide video data, it will fail. If this happens, the host is still not aware of the failure because communication could not be established. With this in mind, the USB Type-C standard requires an embedded device on the monitor or the device side as a failsafe, also known as a notification device. The signer sends a signal to the host computer via the USB 2.0 standard on the D+ and D- lines where communication cannot be established. Then, the host will notify the user that the two devices are not compatible (Figure 5). The notification device will generally be an MCU, possibly the same as the PD controller.

Realize old equipment to transfer Dongle to play the role of power negotiation

If users want to use older peripherals that do not support USB Type-C, they need to use a conversion cable or Dongle. There are a few points to explain, the first being a simple USB 2.0 to Type-C. Since USB 2.0 does not support higher speeds and does not require voltages or currents above 5V or 3A on Vbus, the cable only needs to send D+/D-, Vbus and GND to the header. What is more difficult is how to develop a Type-C to Type-C cable, convert USB 3.0/1 to a Type-C Dongle, or a device that requires a voltage or current of 5V or 3A or more on the Vbus.

How to solve various problems in the development of USB Type-C applications

In these cases, the Dongle becomes part of the power negotiation between the two devices, requiring the cable or Dongles to have an embedded PD controller. The PD controller initially supplies power through the Vbus or Vconn line set to 5V, and then negotiates with the host to reach an agreement on the power supply in the Vbus line. Figure 6 shows an electronically marked cable assembly, or EMCA example, connecting two Type-C devices together. The power supply of the PD controller can be provided by Vconn1 or Vconn2. The EMCA will inform it of its maximum power capacity on the CC line, and the power supply will adjust accordingly.

Alternate Mode is an extension of the Type-C interface that allows Display Port, PCIe or other protocols to use USB 3.1 SuperSpeed ​​cables. When the adapter is connected to a compatible host, it will enter alternate mode. Dongles that support alternate mode require additional precautions and embedded devices. The dongle must tell the host whether it can enter alternate mode to avoid no-message errors.

Dongle notifies via a signer, while the USB Type-C PD standard authorizes any alternate mode accessory to implement signer. Figure 6 shows a cable that converts legacy video ports to Type-C. If the Type-C device does not support the legacy video format, the PD controller will notify the notification device, which will then notify the Type-C device of the error condition.

How to solve various problems in the development of USB Type-C applications

More complex than the DisplayPort/Type-C to Type-C is the docking station or hub, which must support the charging of many devices. A hub can be a combination of multiple Type-C or Type-A ports, HDMI, PCIe, etc. (Figure 7). This hub requires multiple embedded devices to successfully support connected devices. The amount of power required for each port varies depending on the connected device. With this in mind, one PD device may be required per port.

How to solve various problems in the development of USB Type-C applications

Any video port (eg DisplayPort, VGA, or HDMI) requires a signage device. Additionally, hubs require devices to control traffic to the host. This is not much different from Type-A hubs, as collisions on the line must be avoided and only one device communicates with the host at a time. Obviously, compared to the previous simple hub, the design requirements are now more complex and more stringent. The more complex design burden does not need to be entirely undertaken by the developer. Silicon Labs provides development boards, PD libraries, signage source code, and example code for Dongles, docking stations, and device ports. Customers using these tools when developing new Type-C devices can significantly reduce the time and effort invested in USB Type-C development.

Development Board Solutions Simplify Type-C Design

Below is a development board from the company that implements a VESA DisplayPort Alternate Mode Adapter with charging capabilities. Similar development devices can provide power, charging, and video transmission through a single port, thereby increasing the functionality of a single Type-C port on the host. There are two PD controllers on the board, one will be used for each port, and the signage will be used with DisplayPort through the other. The reference design handles switching to alternate modes, charging, notifying the host of error conditions, and ensuring proper power delivery to the Display port and host.

Starting with a development board (Figure 8), working on the provided firmware is lighter and faster than building a new platform and writing the firmware from scratch. This allows manufacturers and suppliers to provide Type-C solutions with more functionality and faster speeds than the competition.

The company’s MCUs (eg Busy Bee3) simplify Type-C design, pack PD functionality into a single 3x3mm2 chip, and provide precision shocks, hardware PD PHY levels, and low bill of materials for customers Cost PD Solutions.

The Universal Bee1 used in the reference design is a single-chip solution that provides signage functionality. Integrated voltage regulators, precision oscillators, USB 2.0 PHY level, and ±8KV ESD protection on the USB pins enable this 3×3mm2 device to perform the signaling function without the need for external components.

USB Type-C is the standard for future trends. Gone are the days of finding the right adapter or cable end in a drawer full of cables. Looking ahead, when choosing a cable, you need to determine whether the cable is a plug or a socket, and whether the cable can handle higher power.

Smartphones, tablets and laptops with only Type-C ports are already on the market, and these pioneering devices are just the beginning. Nevertheless, Type-C also requires embedded devices and firmware to handle a large number of functions, which also puts a lot of pressure on developers and manufacturers to move devices, and Silicon Labs has reference designs, libraries, firmware and a support team that can specifically help simplify the needs of Type-C across a wide range of applications.

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