USB type-C pin signal and PCB layout and wiring
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Usb-type-c is a relatively new standard, providing high-speed data transmission of up to 10Gb / s and power of up to 100W. It can make usb-c a truly universal connection standard for modern devices.
There are three main functions:
● it has a reversible connection interface. The interface is designed so that the plug can be turned relative to the socket.
● it supports USB 2.0, USB 3.0 and USB 3.1 Gen 2 standards. In addition, it can support third-party protocols such as DisplayPort and HDMI in an operation mode called alternate mode.
● it allows the equipment to negotiate and select the appropriate power flow through the interface.
The USB type-C signal connector has 24 pins. Shows the pins of the USB type-C socket and plug.
USB 2.0 differential pair, D + and d-pins are differential pairs for USB 2.0 connection. There are two D + pins and two d-pins in the socket. However, these pins are connected to each other, and actually only one USB 2.0 data differential pair is available. Redundant design is only to provide flippable connectors.
Power and ground pins
The VBUS and GND pins are the return paths for power and signals. The default VBUS voltage is 5 V, but the standard allows the device to negotiate and select the VBUS voltage instead of the default value. Power transmission allows VBUS to have voltages up to 20 v. The maximum current can also be increased to 5A. Therefore, the USB type-C can provide a maximum power of 100 W.
High power flow may be useful when charging large devices of notebook computers. Figure 3 shows an example of Richtek in which the buck boost converter is used to generate the appropriate voltage requested by the laptop. Power transmission technology makes USB type-C more general than the old standard because it adapts the power level to the needs of the load. You can use the same cable to charge your smartphone and laptop.
RX and TX pins
There are two sets of Rx differential pairs and two sets of TX differential pairs.
One of the two RX pairs and the TX pair can be used for the 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.
Note that the USB type-C port can support the 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. The function can even take advantage of all available Rx / TX differential pairs.
CC1 and CC2 pins
The pin is a channel configuration pin that performs 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. How CC1 and CC2 pins display the socket / plug direction. DFP stands for downstream facing port, which acts as 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. CC1 pin of DFP is connected to 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, monitoring the voltage on the DFP CC1 and CC2 pins can determine the cable connection and its direction. In addition to the cable direction, the RP Rd path is also used as a means of transmitting 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.
As mentioned above, USB type-C is designed to provide ultra fast data transmission speed and high level of power flow. 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, the circuit inside the cable can be powered by applying a 5 V, 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. The valid RP Rd path corresponds to CC1 pin. Therefore, the CC2 pin is connected to the power supply represented by vconn.
USB power supply
Briefly introduce USB power supply and standby mode. Devices using the USB type-C standard can negotiate and select an appropriate level of power flow through the interface. These power negotiations are implemented through a protocol called USB power delivery, which is the single line communication on the CC line discussed above. Shows an example USB power supply where 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. The receiver then 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.