Automotive Electro-Static & Surge Design and Test
Author: Shanghai Lei Mao Electronic Technology Co., LTD
China's requirements on automobile EMC’s are becoming increasingly standard and strict. Major automobile manufacturers and testing agencies have been getting more and more understanding about car products. Now automobile electronic products are emerging one after another and the functions are easy to realize, but EMC problems often plague our R&D engineers.
Lei Mao analyzed the EMC test items and key points of design demanded by typical on-board electronic products one by one; hopefully, it will help R&D engineers a little.
Now many on-board products use smart bus terminals: intelligent information collection terminals with advanced Internet of Things and mobile internet technology. The following is a list of a manufacturer's vehicle-mounted information board card related to the communication interface.
one route, 100Mbps
2 routes (one route is used to transmit touch signals)
one route, USB 2.0 OTG
1 route (installed in PAD)
Hard Disk Interface SATA-II
HD Video Input
2 routes (one route is used for PAD screen)
2 routs, each route ≥10W
· 8～40V DC, it has functions of low-voltage protection, overvoltage protection, reverse polarity protection
GB/T 21437.2-2008 Road vehicles - electrical disturbance caused by conduction and coupling - Part 2：Electrical transient conduction along the power line IDT. ISO7637-2:04; Level 3 requirements;
ISO10605:2008 Road vehicles. Electrostatic discharge-generated electricity harassment test method
Question 1: With so many communication interfaces in the table above, which ones need to go throughstatic discharge testing?
Answer: The whole machine first needs to go through the electrostatic discharge test. Any metal or non-metal interface that is accessible to the outside world needs to be tested for static electricity. Insulated electrical interfaces should go through an air discharge test instead of a direct contact test. The voltage level of general air discharge should be higher than that of contact discharge.
Question 2: What is the electrostatic test level of vehicle electronic products?
Answer: At present, the test level of the product is the contact discharge of ±15kV and air discharge of ±25kV.
Question3:Which interfaces need to test ISO7637-2?
Answer: Various requirements of ISO7637-2 include many waveforms such as P1A, P1B, P2, P3A, P3B, P4, P5A, and P5B. These are all to test the anti-disturbance degree of on-board products’ power ports against external power interference, so only the power ports need to be tested.
1. CAN / RS232/ RS485Connection Protection Plan
Two plans are provided by CAN, as shown in the picture above. The integrated solution of SMC24 SOT-23 is adopted to protect cable CAN-H and cable CAN-L. Under the agreement of RS232, it can be replaced by SMC12 SOT-23 or SD12C SOD-323. Alternatively, it can be designed as an integrated solution of SM712 SOT-23 under the agreement of RS485.
2：USB/RJ45/SATA -- Protection Plan of High-Speed Signal Port
Due to the high volume of customer product shipments, we recommend the single-path device protection scheme which can be implemented at low cost. The ultra-low capacitance ESD device is used to protect the high-speed signal port. The devices that can be selected here include PESD0542U005, PESD0563U005, etc. They are all the devices encapsulated with 0.05pF parasitic capacitance of 0402 and 0603. (?)
3：HDMI/ VGA--Protection Plan of Audio and Video Connection Port
The ULC0524P, ULC0544P10, and ULC0514P10 encapsulated with DFN2510 are adopted to meet the electrostatic protection requirements of HDMI1.4 HDMI2.0, as well as the standards for the eye diagram test.
4：Static and Parabolic Load Protection Test of Power Supply Interface
Chart One. TVS Test Results of 12V System
ISO 7637 Test Pulse 5A
80 (JASO standard)
Chart Two. TVS Test Results of 24V System
ISO 7637 Test Pulse 5A
5. How to Set the Testing Machine
There are various types of 7637 test instruments, but it is very important to pay attention to the test results. Capture the waveform by setting the oscilloscope to the corresponding voltage and current.
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