• USB Type-C interface test scheme

    • source: ivan;
    • Time: 9/15/2020 9:58:08 AM
  • USB Type-C interface is a brand new USB interface emerging in recent years. It supports positive and negative symmetric insertion and thin interface, which can support thinner and thinner devices and make portable devices thinner and smaller. USB Type-C interface supports USB 3.1 Gen2, with fast transmission speed, compatibility with USB2.0, and strong power supply capacity. It can support DP 4lane video output through alternative mode. This paper puts forward a solution for USB Type-C interface test in principle, hoping to provide reference for related research.

    0 The introduction

    With the continuous development of USB technology, the application scope of Type-C device is gradually expanded. It supports USB 3.1 Gen2, with the speed up to 10 Gbps, alternative mode and DP 4lane display. This requires a complete solution that can test Type-C device. In this context, this paper focuses on a solution for USB TYPEC interface testing.

    1 Principle and model based on testability of Type-C interface

    USB Type - also known as USB - C or C Type - C, is a new form of universal serial bus hardware interface, USB is standardization organization in order to solve the USB port for a long time do not have a unified physical interface specification, defects such as power can only be one-way transmission of a new interface, its biggest characteristic is its appearance on the top and bottom side completely consistent, support for positive and negative into two directions, users no longer have to distinguish between positive and negative USB, and it sets charging, display, data transmission and other functions in one.

    Type-c interface has a total of 24 pins, 12 on both sides, 4 pairs of TX/RX differential wires,2 pairs of USB D+/ D-signals, 1 pair of SBU,2 CC signals, and 4 VBUS and 4 ground wires. Table 1 shows the PIN signal definition of Type-C.

    The main principles of Type-C are as follows. Under normal circumstances, only one side of the USB 2.0 differential signal will be connected, because THE USB Type-C Plug has no B6 or B7. USB 3.1 only USES 2 pairs of TX/RX differential lines as data lines, connecting TX1/RX1 in positive interpolation and TX2/RX2 in reverse interpolation. In any case, there will be 2 pairs of difference lines that are not used, and DP alternate mode is to load DP signals onto these 2 "redundant" difference lines, so that USB 3.1+DP can work at the same time.

    If the receiving end only needs DP signal and does not need USB 3.1 signal, then DP can make use of all 4 pairs of TX/RX differential lines for output, thus realizing DP output at most 4lanes, providing the total output bandwidth of up to 32.4 Gbps, easily realizing 5K×3K 60 auxiliary video and even up to 8K×4K 60 frames of video. This mode is DP only mode.

    In addition, in order to be compatible with USB 2.0, TYPE-C retains THE USBD+/ D-signal for USE by USB 2.0 devices, so it only needs to use type-C interface. USB 2.0 and even USB 1.0 devices can also support both sides insertion. It is worth mentioning that using USBD+/ D-with DP Only mode above can realize DP+USB 2.0 mode. DP occupies 4 pairs of TX/RX differential wires and USB only USES D+/D-.

    Type-c also provides 2 CC lines and 2 SBU lines. CC line is mainly used for the communication of Power Delivery module. CC line is first used to judge the insertion direction of the device: positive insertion into reverse insertion. If it is positive insertion, the host USES CC1 to communicate with the device; reverse insertion USES CC2, and CC USES single-wire protocol. When the DP function is on, the SBU line is transformed into the AUX_P/AUX_N difference line in the DP protocol (its polarity can be modified according to the direction of positive and negative insertion), which is responsible for transmitting key information such as DPCD and EDID of the equipment.

    2 A solution for USB Type-C interface testing

    This test plan is to provide a solution for verifying USB 3.1Gen2, USB 2.0, DP 4lane signal and power supply capability of USB Type-C UUT devices under test. The test mainly covers the following points.

    Type-c supports data transfer rates of USB 2.0, USB3.1 Gen L, and USB3.1 Gen2. SuperSpeed USB differential signal pairs are allocated on both sides of the interface, so a set of SuperSpeed USB signals are used to transmit connections when plugged into the interface in either direction. This scheme can test one set of USB 3.1 Gen2 signals and USB 2.0 signals respectively.

    Non-usb signal transmission TYPE-C interface supports DP function through negotiation on CC channel. Interface can enter the alternative mode, admiral CC channel coding using the double match number (Biphase Mark Code, BMC) two-way communication with set correctly link, USB 3.1 4 for difference line can be used to transmit DP signal, can transmit 4 lane DisplayPort external DP monitor signal, this scheme support 4 lane DP signal external DP monitor test, with is also supports 2 lane DP turn VGA display test signal.

    When the UUT of the device under test needs to detect a certain voltage on the CC pin, it is determined that SSD, USB 3.1, DP display and other devices have been plugged in or pulled out to provide and manage THE VBUS. When no device is plugged in, close the VBUS. In addition,MUX switches 4 pairs of differential signals to ensure the consistency of signal path impedance, so as to ensure the signal transmission quality. MUX must be controlled by MCU. Meanwhile, CC Logic performs insertion direction detection, and type-C interface is symmetric, so its insertion and unplugging and cable direction can be positive and negative.

    The USB Power Delivery Specification enables the USB Type-C interface to support A voltage of up to 20 V and A current of 5 A. Through USB Power Delivery technology, it can be used for Power supply and Power transmission specifications. The wire standard is DC 5 V, 5 A, and the connector is 3 A. This test scheme provides current testing capabilities up to 5 V and 3 A (the parameters here can be overwritten if the PC can provide additional power output).

    The working process of this test scheme is as follows: The type-C interface of the UUT under test can be tested on USB 3.1 Gen2, USB 2.0, DP 4lane signal and power supply capability by this test scheme. 3 road, USB Type C interface, were calculated with a high speed Crossbar Switch into three USB 3.1 signals or 4 Lane DP signals, 3 USB 3.1 signals respectively to three USB 3.1 connector, 3 Type - C interface of USB 2.0 signals through analog Switch selection Switch to a USB 2.0 1 road signals, to the USB connector, 2.0 3 4 Lane DP signals by DP Switch 1 of 4 Lane DP signals, this 1 4 way Lane DP signals are sent to the DP connector via a 1-turn 2-DP Switch, or 2 lanes in 4Lane are sent to the VGA connector via a DP-turn VGA chip. At the same time, the output current capacity of each VBUS of the 3-way USB TYPE-C interface should be tested (each type-C port can test the power supply of load current of 1a, 2A and 3A respectively when the VBUS is 5 V). In the above process, all the analog Switch switches are controlled through MCU IO and I2C interfaces. In addition, top and bottom surface recognition and upper and lower power control of type-C interface are realized by controlling CC LOGIC Port Controller chip. Taking the upper computer as the control and display terminal, it issues command tests through the upper computer serial port, sends commands through the serial port to test different test items, displays test items and test results, and reports the current status.

    2.1 USB3.1 Gen2 testing

    Support 3-way type-C to 3-way USB 3.1 Gen2, test type-C top and bottom surfaces at the same time. There are 3 TYPE-C and 3 USB 3.1GEN2 test ports in this test scheme, which can support simultaneous testing of 3-way USB 3.1Gen2, and the top and bottom surfaces of THE UUT Type-C interface can be tested by switching through the port controller at the same time. The main features of USB 3.1GEN2 test are summarized as follows:

    ① 3 Type-C connectors, 3 USB 3.1 connectors;
    ② 3-channel Type-C interface to 3-channel USB 3.1 Gen2 interface can be tested at the same time;
    ② The USB 3.1 Gen2 interface speed is up to 10 Gbps, and the Super Speed can be tested with an external SSD or USB 3.1 U disk;
    ③ Type-C to USB 3.1 Gen2 Crossbar Switch can switch the top and bottom surfaces of the USB signal through the MCU;
    ④ The gain of USB 3.1 Gen2 ReDriver is adjustable.

    2.2 USB 2.0 test

    It supports 3-way TYPE-C to 1-way USB 2.0 test. In this scheme, there are 3 TYPE-C interfaces and a USB 2.0 connector. The USB 2.0 signal of 3-way USB Type-C connector is switched to 1-way USB 2.0 signal by analog switch, and USB 2.0 Connector can connect USB 2.0 U disk. The main features of USB 2.0 interface are as follows:

    ① 3 Type-C connectors, 1 USB 2.0 connector;
    ② Type-C to USB 2.0, the maximum interface speed reaches 480 Mbps;
    ③ Only one USB 2.0 signal of 3 Type-C interfaces can be tested at the same time.

    2.3 DisplayPort test

    In this test scheme, the 3-channel USB type-C signal is converted into the 1-channel DP signal through DP Swtich MUX, including 4 lanes. The switch top and bottom surfaces of the 3-channel (A,B,C) type-C signal can be controlled through the port controller, and one of the 3-channel (4) signals can be switched through DP Switch MUX Lane) to DP connector, can be attached to DP display, resolution up to 3120x2160@60PHZ (current DP display support maximum display mode, different DP display support mode is different), at the same time through DP to VGA can be connected to VGA display.

    The following features can be tested for DP:

    ①3 Type-C connectors, 1 DP connector;
    ②Support 3 channels Type-C to 1 channel DP1.2 (lanes) to test the Top and Bottom surfaces of Type-C;
    ③Support DP Mux Switch, support DP1.2 and 4lanes, speed up to 5.4 Gbps;
    ④Type-C to DP Crossbar Switch, supports DP1.4, supports speeds up to 8 Gbps and 4 lanes;
    ⑤DP1.4 ReDriver, support DP1.4:4 channel, speed up to 8.1 Gbps.

    2.4 Port controller

    The USB Type-C interface contains 2 channel configuration (Channel Configu-ration) signal pins (CC1&CC2) for function negotiation. Determine the insertion direction of the interface, and use it to negotiate the power supply function and alternative mode on the interface, support Type-C Port Control (For USB 3.1 Gen2 and DP), control the Crossbar switch and analog switch to control the CC logic chip through the MCU to control the USB Type- For the purpose of C port switching and top and bottom planes, the 3 Type-C interfaces support 3 USB 3.1 Gen2 signals and 3 4 lane DP signal port control.

    The main features of the port controller are as follows:

    ①Three USB 3.1 Gen2 port controllers, switch the Top and Bottom of Type-C USB 3.1 signals;
    ②Three DP port controllers, switch the Top and Bottom planes of Type-C DP signal.

    2.5 Power Delivery power supply capability test

    The default 5 V power supply of the Type-C interface contains 4 pins, which are dedicated for power supply and grounding. The test plan supports Power Delivery with 3 Type-C interfaces, each of which can be powered separately, with currents of 1 A, 2 A, and 3 A. The test is performed when the VBUS is 5 V, and the UUT Type-C port is tested separately. Does the output current have the ability to reach 3 A, and the voltage drop conforms to the USB specification.

    2.6 Power supply of test plan

    The test plan uses a 12 V power supply. The topology of the power supply is as follows: USB 3.1 VBUS comes from UUT Type-C interface VBUS. When the UUT Type-C interface detects that the device (USB 3.1 SSD, U disk, DP device, etc.) is inserted, UUT The VBUS of the Type-C interface of the device will supply power to the VBUS voltage of the test solution.

    2.7 PC software

    The host computer software is mainly an MCU developed for Type-C functional testing, which controls the Crossbar Swtich, analog switch and DP switch respectively, so as to realize the USB 3.1 Gen2, USB 2.0 top and bottom surface of the Type-C interface of the UUT. Detect the voltage conditions under different loads to evaluate the power supply capability of the UUT Type-C interface VBUS, thereby completely testing the UUT's Type-C interface function.

    3 Application examples

    A factory conducts a series of tests on Type-C equipment leaving the factory, including Type-C top, bottom surface, USB 3.1 Gen2 speed, USB2.0, DP monitor display capacity and Type-C VBUS load capacity.

    4 Conclusion

    This article describes a test solution for a new USB Type-C interface. Type-C interface supports positive and negative plugging, slim interface, can support thinner and lighter devices, supports USB 3.1 Gen2, transfer speed up to 10 Gbps, compatible with USB 2.0, can provide 5 V, 3 A power supply capability, through replacement The mode can support DP 4lane video output. From these advantages, it can be seen that Type-C will be more and more widely used in the future, and it is also essential to find a relatively simple test scheme for Type-C functions. The test scheme proposed in this article basically covers Type -C interface application test scenarios, flexible and convenient.