The working principle and technical analysis of USB Type-C－雷克斯の生活日誌

(一) Basic specifications

Comparison of USB names and transmission speeds ↑

Comparison of USB output power and logo in previous generations↑

SS means supporting PD, and SS and 10 USB logo means supporting USB3.1 and PD2.0

(二) Advantages of USB Type C

Comparison of previous generations of USB connector shapes ↑

1. Complete functions: It supports data, audio, and video transmission at the same time, and also supports charging functions, all concentrated on one transmission line, which can solve the problem of too many transmission lines.

2. Support for positive and negative insertion: Type C's pins are mirror image design, which can support positive and negative insertion. There is a special detection mechanism on the hardware to determine whether it is positive or reverse. This part will be mentioned later. (The phone needs to be charged in the middle of the night, no need to turn on the light to see the direction of the connector!)

3. Two-way transmission: Data and electricity can be transmitted and charged in two directions.

4. Backward compatibility: It can be compatible with USB type A, micro B and other interfaces through the dongle.

5. Fast transfer rate: Support USB 3.1, can support up to 10Gbps data transfer.

(三) The functions of USB Type C pins

Pin description：

(1) Tx / Rx: Two sets of differential signal transmission pairs for data transmission.

(2) CC1 / CC2 (Configuration Cannel):

Detect positive and negative plug, detect whether the cable is connected, determine which side is DFP (Downstream Facing Port) and UFP (Upstream Facing Port), configure Vbus, configure Vconn,

Configure other modes (alternate or accessory mode), PD communication, etc. In short, CC manages the communication between the master and slave through the USB type C connection.

(3) Vbus: For power supply, connect CC pin to Vbus

(4) D+ / D-: Support USB2.0 downward.

(5) SBU1 / SBU2: Used to transmit auxiliary signals, DP Alt mode can use this pin to transmit AUX data.

(6) GND: Ground, there are 4 power and ground, so it can support up to 100W.

(四) Working principle and model of CC

(1) DFP (Downstream Facing Port) is the Host side, and the UFP (Upstream Facing Port) on the other side is the device side. In DFP

The CC pin has a pull-up resistor Rp, and the UFP has a pull-down resistor Rd. (Rp determines the power supply capability provided by the host to the device)

(2) When DFP and UFP are not connected, DFP's VBUS is not output. When DFP is connected to UFP, CC pin is connected, DFP’s

CC pin detects UFP pulldown Rd, indicating that it is connected to Device, and DFP turns on the FET switch of VBUS and outputs VBUS power to

UFP, which means that VBUS will not supply any power to the UFP terminal before the CC PIN setting is detected.

(3) It can be clearly seen from the figure above that except for Ra, the other resistances should not appear in the cable. The value of Ra is an interval value as shown in the table below. Generally, 1k ohm is used, such as a power supply The wire may be slightly lower than 800 ohm:

Resistance value range of Ra↑

(4) The value of Rp is regulated. At present, the common 56k ohm is regulated as the default USB power, which is generally used to be compatible with the traditional USB architecture. Therefore, the type A/B to type of USB2.0/USB3.0 often appears For the wire of C, add this resistor to the type C end. Please see the remaining resistance values

Table below:

Resistance value range of Rp↑

(5) Rd is only 5.1k ohm in the specification and will not be used in cable.

(6) A cable with Ra must have an e-mark IC inside, so it will support the PD protocol. A cable without Ra must be a passive cable. There is no IC inside, and of course the PD protocol must not be supported.

(7) CC pin detection can be divided into the following results:

(8) Positive and negative insertion detection

Since Type-C supports positive and negative plugs, the CC pin is used to detect positive and negative plugs. From the perspective of DFP, when CC1 is connected to Pulldown (Rd), it is positive plug, and if CC2 is connected to Pulldown, it is reverse plug. After detecting the positive and negative plug, the corresponding USB signal will be output, for example, CC1 corresponds to SSTX1 and SSRX1. The right side of the figure below integrates MUX. Since the data rate of USB 3.1 is as high as 10 Gbps, in order to avoid PCB wiring branching, the signal inserted in the front and back will be switched by MUX. When it is plugged in, switch to SSRX1&SSTX1, and plug in reverse. When, switch to SSRX2&SSTX2.