Ⅰ. What is USB-Type-C?

1. The meaning of USB-Type-C

USB Type-C is a smaller-volume USB interface standard than Type-A and Type-B. It can be used on a PC (master device) as well as external devices (slave devices, such as mobile phones). type.

4 pairs of TX/RX split lines, 2 pairs of USBD+/D-, a pair of SBU, 2 CCs, 4 VBUS, and 4 ground wires make up USB Type-C. USB-C is a relatively new standard that allows for high-speed data transmission of up to 10 gigabits per second and power of up to 100 watts. These features have the potential to make USB-C a truly global connector for current electronics.

2. Function introduction

The USB-C interface serves three purposes:

The connection interface is reversible. The plug can be flipped in relation to the socket due to the interface's architecture.

It complies with USB 2.0, USB 3.0, and USB 3.1 Gen 2 specifications. In addition, it has an operating mode called Alternate Mode that allows it to accept third-party protocols like DisplayPort and HDMI.

Through the interface, devices can negotiate and select the appropriate power flow.

3. Signal Diagram

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

Note: The characteristics of the USB Type-C interface are as follows:

A. Compact: Unlike the common USB Type-A interface, the new USB Type-C interface is much smaller, measuring only 8.3*2.5mm, making it more suitable for increasingly downsized computing. It can resist 10,000 repetitions of plugging and unplugging when used in equipment.

B. High data transmission speed: USB3.1 specification support, data transmission speed up to 10Gbps;

C. Non-directional: The USB Type-C interface, like the Apple Lightning interface, has no directional constraints, meaning that pairing can be completed by inserting both the front and back sides, considerably improving the USB interface's simplicity of use.

D. Strong power supply capability: The USB3.1 Type-C interface can give up to 100W of power output, and the USB Typc-C interface can provide two-way power supply: it can charge the device or supply power to external devices while also charging the device. The time can be cut in half to two thirds;

E. High scalability: USB Type-C can carry audio and video signals, as well as grow to a number of audio and video output interfaces, including HDMI, DVI, and VGA, and even support 4K resolution expansion.

Ⅱ. USB 2.0 differential pair

For USB 2.0 connections, the D+ and D- pins are differential pairs. In the socket, there are two D+ pins and two D- pins.

However, because these pins are coupled to one another, there is only one USB 2.0 data differential pair that can be used. The redundant design is solely for the purpose of providing a reversible connector.

Ⅲ. Power and ground pins

The VBUS and GND pins are the power and signal return channels. The default VBUS voltage is 5V, although the standard permits the device to negotiate and choose a different VBUS voltage than the default. VBUS can have a voltage of up to 20V thanks to power transmission. It is also possible to boost the maximum current to 5A. As a result, USB Type-C can deliver up to 100W of power.

High power flow may be beneficial for charging large devices such as laptop computers. Figure 3 depicts a RICHTEK example in which a buck-boost converter is utilized to create the voltage that the laptop requires.

Because the power transfer technology adapts the power level to the needs of the load, USB Type-C is more versatile than the old standard. You can charge your smartphone and laptop with the same wire.

Ⅳ. RX and TX pins

RX differential pairs and TX differential pairs are divided into two groups.

For USB 3.0 / USB 3.1 protocols, one of the two RX pairs and the TX pair can be used. The multiplexer is required to correctly redirect the data on the utilised differential pair across the cable because the connector is reversible.

Please note that while the USB Type-C port can handle the USB 3.0/3.1 standard, USB 3.0/3.1 is not included in the USB Type-C minimum feature set. Other USB Type-C capabilities, such as standby mode and USB power supply protocol, can use the USB 3.0/3.1 connection instead of the RX/TX pair in this instance. These routines can even use all RX/TX differential pairs that are available.

Ⅴ. CC1 and CC2 pins

These pins are used to configure the channel. They have a variety of purposes, including detecting cable connections and removal, socket/plug orientation detection, and current broadcast. These pins can also be used for Power Delivery and Alternate Mode communication.

The CC1 and CC2 pins display the socket/plug orientation in Figure 4. DFP stands for downstream facing port in this diagram, which serves as a host or power source during data transfer. Upstream facing port (UFP) refers to a device that is linked to a host or power consumer.

The Rp resistor pulls up the CC1 and CC2 pins in DFP, but Rd pulls them down in UFP. The source detects a logic high level at the CC1 and CC2 pins if the cable is not attached. By connecting the USB Type-C cable to the 5V power supply, a current route from the power supply to the ground is created. Because the USB Type-C cable only has one CC wire, just one current path is produced. The CC1 pin of the DFP, for example, is connected to the CC1 pin of the UFP in the upper diagram of Figure 4.

As a result, the DFP CC1 pin voltage is less than 5 V, yet the DFP CC2 pin remains at a logic high level. As a result, we can determine the cable connection and direction by monitoring the voltage on the DFP CC1 and CC2 pins.

In addition to conveying information about the cable's orientation, the Rp-Rd path is also utilized to send information about the source's present capability. The power consumption (UFP) monitors the voltage on the CC line to achieve this. The source can offer the default USB power supply of 500 mA and 900 mA for USB 2.0 and USB 3.0, respectively, when the voltage on the CC line is at its lowest value (about 0.41 V). The source can generate 1.5 A of current when the CC line voltage is around 0.92 V. The greatest CC line voltage is around 1.68 V, corresponding to a 3A source current capability.

Ⅵ. VCONN pin

USB Type-C intends to provide ultra-fast data transfer speeds and high levels of power flow, as previously stated. These qualities may need the usage of special cables with a chip inside that is electronically tagged. Furthermore, some active cables include re-drive chips to boost the signal and compensate for the cable's loss. In these circumstances, a 5 V, 1 W power supply to the circuit inside the wire can be used to power the VCONN pin. Figure 5 illustrates this.

As you can see, the active cable pulls the CC2 pin down using the Ra resistor. DFP can still determine cable orientation by monitoring the voltage on the DFP CC1 and CC2 pins because Ra is different from Rd. The channel configuration pin corresponding to the "active cable IC" will be linked to a 5 V, 1 W power supply to supply power to the circuit inside the cable after the cable's direction has been determined. The effective Rp-Rd route, for example, corresponds to the CC1 pin in Figure 5. As a result, the CC2 pin is linked to the VCONN power source.

Ⅶ. SBU1 and SBU2 pins

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

Ⅷ. USB powered

Let's take a look at the USB power supply and standby mode after we've gotten a handle on the USB-C standard's fixation.

Devices that use the USB Type-C standard can negotiate and select an acceptable degree of power delivery across the interface, as previously described. These power negotiations are accomplished using the USB Power Delivery protocol, which is the single-wire communication on the CC line mentioned earlier. Figure 6 depicts an example USB power supply, in which the receiver issues a request to the source, which then adjusts the VBUS voltage as needed. First and foremost, a 9V bus is necessary. It will transmit a "power ready" message to the receiver after the source bus voltage has stabilized at 9V. The receiver then demands a 5V bus, which is provided by the source, which then sends the "power ready" message once more.

It's worth noting that "USB power supply" refers to more than just power supply; other agreements, such as those for standby mode, are also carried out using the power supply protocol on the standard CC line.

Ⅸ. PCB design and wiring requirements

The Type-C interface layout and wiring requirements:

1) ESD, the common-mode inductance device is close to the USB interface, the order of placement is ESD-common mode inductance-resistance and capacitance; also pay attention to the distance between ESD and USB, leave a 1.5mm spacing, consider the situation of post welding.

2) Type-Ce has four sets of differential signals RX/TX1-2, two sets of D+/D- differential signals, a total of six pairs of differential lines. Differential signal lines are required to be adjacent to at least one ground plane, and it is best if both sides are adjacent to the ground plane.

3) Ensure that the line spacing of the differential line is consistent during the routing process. The differential line should be as long as possible. If the length of the two lines is different, you can draw a serpentine line to increase the length of the short line.

4) CC1/CC2 are two key pins, which have many functions: detect the connection, distinguish the front and back, distinguish DFP and UFP, that is, the master-slave configuration Vbus and the surface should be thickened when routing.