Very detailed introduction to USB Type-C Pin signal and PCB layout and wiring

At present, the intelligent terminal market has formed a pattern dominated by USB-C interface and the coexistence of various interfaces and charging technologies. After the user changes the equipment, most of the original chargers and data lines are idle, resulting in huge waste. Vigorously promoting the integration of charging interface and technology is conducive to reducing e-waste and improving resource utilization efficiency. In fact, it is not difficult to see that the state has been promoting the reform of charging interface. Some time ago, Netease CEO William Ding suggested to the Ministry of industry and information technology that "unify the standard port of smart electronic device charger to further reduce E-waste and help carbon neutralization." The future of USB Type-C unified trend is unstoppable.

Type-C Knowledge

USB Type-C is the specification of USB connector system. It is more and more popular in smart phones and mobile devices, and can transmit power and data. USB-C is a relatively new standard. The current version is USB4. The USB4 specification uses dual link channels, with a transmission bandwidth of up to 40Gbps and a power of up to 240W. These functions can make USB

-C a truly universal connection standard for modern devices.

Signal diagram of USB Type-C main function introduction

The USB Type-C connector has 24 pins. Figure 1 and Figure 2 show the pins of USB Type-C socket and plug respectively.

PCB design and wiring requirements of USB Type-C

Power supply and standby mode of USB Type-C

Devices using USB Type-C standard can negotiate and select the appropriate power through the interface. These power negotiations are realized through a protocol called USB power delivery, which is the single line communication on the above CC line. The following figure shows an example USB power supply in which the receiver sends a request to the source and adjusts the VBUS voltage as needed. First, a 9 V bus is required. After the source stabilizes the bus voltage to 9 V, it sends a "power ready" message to the receiver. Then, the receiver requests a 5V bus, and the source provides it and sends the "power ready" message again. It is worth noting that "USB power supply" involves not only negotiations related to power supply, but also other negotiations, such as those related to standby mode, are completed using the power supply protocol on the standard CC line.

CC1 and CC2 pins of USB Type-C

These pins are channel configuration pins. They perform many functions, such as cable connection and removal detection, socket / plug direction detection and current broadcast. These pins can also be used for communication required by power delivery and alternate mode. The following figure shows how CC1 and CC2 pins show the socket / plug direction. In this figure, DFP represents the downstream facing port, which acts as the host or power supply in data transmission. UFP means upstream facing port, which is a device connected to the host or power consumer. DFP pulls up CC1 and CC2 pins through RP resistance, but UFP pulls them down through Rd. If no cable is connected, the source sees a logic high level at CC1 and CC2 pins. Connecting the USB Type-C cable creates a current path from a 5V power supply to ground. Since there is only one CC line in the USB Type-C cable, only one current path is formed. For example, in the figure, the CC1 pin of DFP is connected to the CC1 pin of UFP. Therefore, the voltage of DFP CC1 pin is lower than 5 V, but DFP CC2 pin is still at logic high level. Therefore, by monitoring the voltage on the DFP CC1 and CC2 pins, we can determine the cable connection and its direction.

In addition to the cable direction, the RP-Rd path is also used as a way to transmit source current capability information. For this purpose, the power consumption (UFP) monitors the voltage on the CC line. When the voltage on the CC line has its lowest value (about 0.41 V), the source can provide 500 mA and 900 Ma default USB power for USB 2.0 and USB 3.0, respectively. When the CC line voltage is about 0.92 V, the source can provide a current of 1.5 a. The maximum CC line voltage is about 1.68 V, which corresponds to the source current capacity of 3A

Vconn pin of USB Type-C

USB Type-C is designed to provide ultra fast data transmission speed and high level of power. These features may require the use of special cables for electronic marking through the internal use of chips. In addition, some active cables use the re drive chip to strengthen the signal and compensate the loss caused by cables, etc. In these cases, we can supply power to the circuit inside the cable by applying 5V and 1 W power supply to the vconn pin. The active cable uses a ra resistor to pull down the CC2 pin. The value of RA is different from RD, so DFP can still determine the cable direction by checking the voltage on DFP CC1 and CC2 pins. After the cable direction is determined, the channel configuration pin corresponding to the "active cable IC" will be connected to the 5 V, 1 W power supply to supply power to the circuit inside the cable. For example, in the figure below, the effective RP Rd path corresponds to CC1 pin. Therefore, the CC2 pin is connected to the power supply represented by vconn.

SBU1 and SBU2 pins of USB Type-C & RX and TX pins

SBU1 and SBU2 pins

These two pins correspond to the low-speed signal path used only in standby mode.

RX and TX pins

There are two sets of Rx differential pairs and two sets of TX differential pairs.

One of these two RX pairs and TX pair can be used for USB 3.0 / USB 3.1 protocol. Since the connector is reversible, the multiplexer needs to reroute the data on the differential pair correctly through the cable.

Please note that the USB Type-C port can support USB 3.0 / 3.1 standard, but the minimum feature set of USB Type-C does not include USB 3.0 / 3.1. In this case, the USB 3.0 / 3.1 connection does not use Rx / TX pairs and can be used by other USB Type-C functions, such as standby mode and USB power supply protocol. These functions can even take advantage of all available Rx / TX differential pairs.

Power and ground pins of USB Type-C

VBUS and GND pins are the return paths of power supply and signal. The default VBUS voltage is 5V, but the standard allows the device to negotiate and select the VBUS voltage instead of the default value. Latest PD3 1 protocol, the power transmission allows VBUS to have a voltage of up to 48V, and the maximum current of USB4 can also be increased to 5A at present. Therefore, USB Type-C can provide a maximum power of 240W. High power is useful when charging large devices such as laptops.

USB 2.0 differential pair for USB Type-C

The D + and D-pins are differential pairs for USB 2.0 connections. There are two D + pins and two d-pins in the socket. In fact, there are only 2.0 pairs of USB pins for mutual connection. Redundant design is only to provide reversible connectors.

Type-C related industrial chains have attracted much attention

Type C interface has many advantages, such as small and slim, high-speed transmission, positive and negative availability, one port multi-purpose, power supply improvement and so on. Its popularization will be just around the corner. However, this Type C connector product must play in a limited space, make more refined products with a wide range of functions, and must bear high current and carry out high-speed data transmission. Therefore, its technical difficulty requirements are very high, and challenges and opportunities coexist. For those enterprises eager to seize the Type C connector market, only by solving technical problems then can win customers and market.