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The Working Principle And Technical Analysis Of USB Type-C

The further application of USB Type-c started with USB3.1 because, from USB3.1, THE functions of USB began to become richer.

Table of Contents

The further application of USB Type-c started with USB3.1 because, from USB3.1, THE functions of USB began to become richer.

① USB 3.1 Basic specifications

GenerationMbpsUSB Gen. NamePowerLaunch Time
USB 1.01.5 MbpsLow Speed500 mAJan. 1996
USB 1.112 MbpsFull Speed500 mASep. 1998
USB 2.0480 MbpsHigh Speed500 mAApr. 2000
USB 3.05 GbpsSuperSpeed Gen1900 mANov. 2008
USB 3.110 GbpsSuperSpeed Gen2900 mAAug. 2013
USB Speed chart
The mark SS indicates that PD is supported. The mark SS and 10 indicates that USB3.1 and PD2.0 are supported

② Comparison of USB output power and logo in past dynasties


1) Fully functional: support data, audio, and video transmission, but also support charging function, all concentrated in a transmission line, can solve the problem of too many transmission lines.

2) Support positive and negative insertion: The pin position of Type C is a mirror design, which can support positive and negative insertion. The hardware has a special detection mechanism to determine whether it is a positive or negative insertion, which will be mentioned later. (You don’t need to turn on the light to check the connection direction to charge your phone in the middle of the night!)

3) Bidirectional transmission: data and power can be bidirectional transmission and charging.

4) Downward compatibility: through a dongle, compatible with USB type A, MICRO B, and other interfaces.

5) The fast transmission rate supports USB 3.1 and can support up to 10Gbps data transmission.

③ USB Type C pin function overview

USB Type C Female/male pin position diagram

Foot position description:

(1) Tx/Rx: two sets of differential signal transmission pairs for data transmission.
(2) CC1 / CC2 (Configuration Channel) Detect Downstream Facing Port (DFP) and Upstream Facing Port (UFP), configure Vbus, CONFIGURE Vconn, and configure alternate or Accessory mode, PD communication, etc. In a word, CC manages communication between master and slave via USB Type C wiring.
(3) Vbus: Power supply, CC pin-connected, Vbus power supply
(4) D+ / D- : supports USB2.0.
(5) SBU1 / SBU2: for transmitting auxiliary signals, DP Alt Mode can use this pin to transmit AUX data.
(6) GND: grounding, power supply, and grounding have four, so it can support up to 100W.

④ CC working principle and model


(1) The Downstream Facing Port (DFP) is the Host end and the Upstream Facing Port (UFP) on the other side is the device end. The 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 of the host terminal to the device terminal)

(2) When DFP and UFP are not connected, the VBUS of DFP has no output. After the DFP and UFP are connected, the CC pin of the DFP detects the PULLdown Rd of the UFP, indicating that the device is connected. Then the DFP turns on the FET switch of the VBUS and outputs VBUS power to the UFP. That is to say, before the setting of the CC pin is detected, The VBUS does not supply any power to the UFP.

(3) It can be clearly seen from the figure above that resistances except Ra should not appear in the cable. Ra value is an interval value as shown in the table below. Generally, 1K Ohm is used, and the wire used as a power supply may be slightly lower than 800 Ohm: Ra resistance range


(4) The value of Rp is standardized. The current common 56K Ohm is standardized as default USB power, which is generally compatible with the traditional USB architecture. Therefore, it often appears that the cable of TYPE A/B to Type C of USB2.0/USB3.0 is added with the resistance at the end of Type C. Please see other resistance values

Table below:


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

(6) All cables with Ra must have an e-mark IC inside, so they all support PD protocol. A cable without Ra must be a passive cable, and there is no IC inside. Of course, it must not support PD protocol.

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


(8) Positive and negative detection: Since Type-C supports positive and negative insertion, a CC pin is used to detect positive and negative insertion. From the perspective of DFP, if CC1 receives Pulldown (Rd), it is a positive insertion, and if CC2 receives Pulldown, it is reverse insertion. After the detection of the positive and negative plugs, the corresponding USB signal will be output, for example, CC1 corresponds to SSTX1 and SSRX1. The right side of the figure is integrated with MUX. Since the data rate of USB 3.1 is as high as 10 Gbps, in order to avoid the branching of PCB wiring, the signals of positive and negative insertion will be switched by MUX. In the case of positive insertion, they will be switched to SSRX1&SSTX1, and in the case of reverse insertion, they will be switched to SSRX2&SSTX2.

Schematic diagram of Data transmission path (blue line is a forward interpolation, the red line is back interpolation)
DiskMFR Field Sales Manager - Leo

It’s Leo Zhi. He was born on August 1987. Major in Electronic engineering, He is an Enthusiastic professional, responsible person, and computer hardware & software literate. Proficient in NAND flash products for more than 10 years, critical thinking skills, outstanding leadership, excellent Teamwork, and interpersonal skills.  Understanding customer technical queries and issues, providing initial analysis and solutions. If you have any queries, Please feel free to let me know, Thanks

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