The Conformance Testing of CAN Bus Transceiver

◎ CAN bus Transceiver Verification

The full-scale launch of electric vehicles in the 21st century is a great revolution in the automobile industry. Automatic driving technology makes traffic more convenient and changes human driving habits. Under the highly electronic vehicle architecture of the control unit, the CAN bus is one of the key communication interfaces. There are three ways to evaluate the methods ensuring high interoperability between CAN bus transceiver and transceivers with different functions in the vehicle environment: 　

As shown in Figure 1, there are three ways to verify the performance and interoperability of CAN bus transceivers in relative environments, including transceiver monomer electrical properties, single node electromagnetic compatibility performance evaluation and multi-node interoperability assessment. In terms of the transceiver monomer, it is used to verify whether it meets the electrical properties required by the relevant standards of the International Organization for Standardization (ISO) and the International Society of Automotive Engineers (SAE International). The single node uses the SAE International standard to evaluate the electromagnetic interference and tolerance under the relative environment, and the multi-node method is used to evaluate the interoperability performance of different functional transceivers at the specified communication rate. In addition to the self-assessment method, relevant reports can also be obtained after verification and assessment by international mainstream car manufacturers or third-party laboratories recognized by T1 suppliers.

◎ Conformance Test Plan

The latest version of the CAN bus high-speed physical layer standard is ISO 11898-2:2016[1], which defines the use of serial communication protocols to support distributed real-time control and multiplexing for road vehicles. Except for standardizing its electrical characteristics behaviors, it is required to refer to ISO 16845-2:2018[2] standard for a conformance test plan. The conformance test plan defines the type and setup of the test. The conformance test is a test process used to test whether the transceiver components meet the relevant standards to ensure product quality, including static tests and dynamic tests. In CAN network, the inconsistent quality of each ECU can lead to problems such as errors, network failures or network downtime. Therefore, in order to ensure the normal and safe operation of the CAN bus network, its components must be tested for conformance. 

Static test is performed in a reference environment using predefined settings to ensure a high degree of repeatability and comparability of test results. During the test, relevant parameter of CAN bus transceiver specifications and maximum/minimum values defined by electrical property are checked for complying standard requirements. The expected test results must meet the electrical properties and limit value ranges of ISO11898-2:2016.Figure 2 below shows the default setup requirements for testing and describing the relationship between the input control signal and the output signal of the DUT. Only resistors and capacitors are placed around the components, but no electrostatic protection components are placed [1]. (RL = 60Ω±0.6Ω, C1 = 4.7nF±0.235nF & C2 = 100pF±1pF)

Dynamic testing increases the likelihood and confidence in the interoperability of high-speed CAN transceivers with different functional transceivers within the system. The types included in the dynamic test are shown in Figure 3 below. The CAN bus protocol packet format used in the setup environment will use three different speeds for the data segment that include 500kbit/s, 2Mbit/s and 5Mbit/s. The arbitration segment is maintained at 500kbit/s. For example, AZKN1044T[3] supports variable high-speed data transmission up to 5Mbit/s. In its experimental combination, only 2Mbit/s and 5Mbit/s are required for data segment verification, because the arbitration segment has been implemented at a rate of 500kbit/s. The actual test items are based on the related functions supported by the CAN transceiver itself. For example, the wake-up system provided by the transceiver is used for coordination experiments.  

The experiment assessment uses two networks for test that include homogeneous network and heterogeneous network. Homogeneous network tests include 8 nodes with a data speed of 5Mbit/s network topology and 16 nodes with a data speed of 2Mbit/s network topology. The heterogeneous network test is to mix different CAN bus transceiver brands and network topology experiments at different data transmission speeds. In the experiment of heterogeneous network, it can be determined whether there will be different test results when it is coordinated with different transceiver manufacturers and the electrical limit values of some parts are different.       

Figure 3: Default test applicability due to device implementation [2]

In addition, 7 main test procedures are introduced in the experiment which is based on all possible combinations of normal operating mode, low  power mode, error and error free. Experiment with failure condition are added, such as CANH or CANL signal open circuit, mutual short circuit between CANH and CANL, CANH or CANL short circuit to the reference ground, CANH or CANL short circuit to the battery power supply, and CANH and CANL signals disconnected at the same time. . By means of several common failure behaviors in actual automotive environment, if CAN transceiver is still undamaged and is able to continue to communicate under the defined behavior when the failure event occurs and returns to normal conditions are simulated.  

Figure 4 is a simulation that after simulating several failures in the third step, the failures are eliminated and returned to normal after at least 1.5 seconds when all ECUs on the bus are in normal mode, The fifth step is to wake up the node through the bus system after entering the power saving mode. At the end of steps 2, 4 and 6 in the process, all nodes must be able to perform the specified behavior of transmission and receiving. 

The complete static and dynamic test plan of the CAN bus transceiver representing a confidence level of interoperability when there are various transceivers in system. It reduces assessment time of system development engineer and obtains high valuation from car manufacturer.

◎ Conclusion

AZKN1044T[3] is a vehicle-grade CAN bus transceiver that complies with ISO11898-2:2016 standard, and supports variable data speed up to 5Mbps and local and remote bus wake-up systems. In addition, the bus port of the transceiver also provides 70V false triggering protection, and the internal surge suppression capability for ISO10605 and ISO7637 series is also provided. The German laboratory C&S (Communication & systems group) verification report has been obtained and can be provided to customers, see Figure 5.We firmly believe that the cooperation with third-party laboratories through a solid product verification system will add credits to your products and create a win-win situation.