The CAN bus design specification has strict regulations on the input voltage threshold of the CAN node. If the input voltage threshold of the node does not meet the specifications, the abnormal working state is likely to occur after the field networking, and communication failure occurs between the nodes. The specific requirements are shown in Table 1, which is the test standard "ISO 11898-2 output voltage standard".
Table 1 ISO 11898-2 input voltage threshold standard
Test parameter test value (V) condition
Minimum value
Dominant Vdiff input voltage 0.92.05.0 bus load resistance 60Ω, common mode voltage (min=-2V, max=7V)
Implicit Vdiff input voltage -100.5 bus load resistance 60Ω, common mode voltage (min=-2V, max=7V)
Therefore, each manufacturer must test the input voltage threshold of the CAN node DUT (device under test) before the product is put into use. Generally, the CAN test method using the ISO 11989-2 input voltage threshold standard is described as follows:
As shown in Table 1, under load and common mode conditions, select the adaptation conditions of the DUT under test, as shown in Figure 1, Rtest is the network load resistance, which is 60Ω.
Adjust U so that V is -2V and 6.5V respectively, then adjust I, so that Vdiff=0.5V, observe whether the DUT can communicate normally. If the communication is normal, pass the recessive Vdiff input voltage test.
Then adjust U so that V is -2V and 6.1V, then adjust I, so that Vdiff = 0.9V, observe whether the DUT can stop communication, if it can stop communication, pass the dominant Vdiff input voltage test.
Figure 1 Input voltage threshold test principle
It can be seen that although the method can measure the input voltage threshold of the CAN node, in order to simplify the operation and improve the accuracy of the measurement result, Guangzhou Zhiyuan Electronics Co., Ltd. improved the test method, using CANScope-Pro bus analyzer, CANScope -StressZ expansion board and programmable DC power supply DCP8325L combination scheme for measurement.
The test plan is as follows:
1. As shown in Figure 2, test the connection. Adjust the RHL value of the CANScope-StressZ analog expansion board to 60Ω, and RH and RL to 0Ω. The DUT actively sends CAN messages, CANScope does not check the bus response, and the black test leads (ground) are shared with the DUT's CAN transceiver.
Figure 2 Input voltage threshold test connection diagram
2. As shown in Figure 3, configure the interference source to be external, then start CANScope and CANScope-StressZ analog expansion board to start testing.
Figure 3 Adjusting the CANScope-StessZ interference source to external
3. Adjust the U of the DCP8325L so that the V is -2V and 6.5V respectively, then adjust the I of the DCP8325L. When observing Vdiff=0.5V from the CANScope oscilloscope, observe whether the DUT can normally send messages. If normal communication, Then the recessive Vdiff input voltage test passes.
4. Then adjust U so that V is -2V and 6.1V respectively, then adjust I, observe Vdiff=0.9V from CANScope oscilloscope, observe whether DUT can stop communication, if it can stop communication, then explicit Vdiff input The voltage test passed.
CANScope Analyzer Guangzhou Zhiyuan Electronics Co., Ltd. develops a comprehensive CAN bus development and testing professional tool, integrating mass storage oscilloscope, network analyzer, bit error rate analyzer, protocol analyzer and reliability test tool. And organically integrate and correlate various instruments; redefine the development and test methods of CAN bus, which can evaluate the correctness, reliability and rationality of CAN network communication in multiple angles; help users quickly locate faulty nodes and solve them. The various problems of CAN bus application are the ultimate tools for CAN bus development and testing.
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