There was an advantage to the old cars I used to drive back many years ago when I was a teenager. They were inexpensive, easy to maintain, and robust enough to take the beating that I put them through. However, they also drank a horrendous amount of gas and oil, were loud and clunky, and left a cloud of pollution behind them. They also had the simplest of electronics within them that would never hold a candle to the benefits offered by today’s advanced automotive electronics.
Other than firing the spark plugs, the electronics in those older cars did little more than power the lights, some of the instruments, and the stereo system, which was a mandatory requirement of any teenager’s car. Today it’s a completely different story with automotive electronics controlling engine emissions, safety and environmental systems, and a host of computer and communications systems as well as entertainment.
To keep these electronics from being affected by external electromagnetic interference (EMI), or affecting each other, automotive electronics today have to meet specific electromagnetic compatibility (EMC) requirements. To do this, electronics designers for automotive products have to understand what those requirements are, and how best to design for them. Here is a little more information on how you can be prepared for designing to the EMI/EMC standards for automotive electronic components.
Why Are the EMI/EMC Standards for Automotive Electronic Components Important?
The modern gasoline-powered automobile is a fascinating mixture of old-school internal combustion engine technology and modern electronics. As such, it is a very fertile ground for EMI problems. These problems can come from either the various external wireless and electrical systems across the country, or from the many different internal electronic systems within the vehicle. The average car may have any number of electronic systems from among the hundreds of different systems available today. These include airbags, engine & transmission controls, antilock braking, cabin environment, instruments & diagnostics, navigation & lighting, and entertainment. All of these systems, if not designed correctly, are susceptible to interference from outside sources, or from the other systems in the vehicle itself.
The EMI that can be generated from the different automotive systems is categorized into narrowband emissions and broadband emissions, also known as “arc and spark.” Broadband EMI is generated by automotive components that arc and spark like ignition and pulse-type systems, as well as electric motors. Narrowband EMI is generated by all of the other active electronics in the automobile. Each of these active systems relies on moving instructions and data through their microprocessors, and any unexpected interruption due to broadband or narrowband EMI can adversely affect the expected function of the system. If this interruption affects a system for controlling the vehicle such as engine or braking controls, the results can be catastrophic. For this reason, establishing standards for automotive EMI and testing for those standards is extremely important.
Automotive EMI/EMC Standards for Testing
There are many different standards for EMI and EMC testing in the automotive industry. Some of these are very broad in nature, while others cover specific areas of testing or targets of the testing. Here are some of the main standards that you will be working with:
- CISPR 12 & CISPR 25: Both of these standards deal with automobiles, and cover the radio disturbance characteristics for the protection of radio receivers. CISPR 12 covers receivers that are not in the vehicle, while CISPR 25 covers those receivers that are on-board. CISPR 12 is commonly used as a regulatory requirement to ensure that automobile internal combustion engines do not interfere with TV and radio reception when the vehicle is in close proximity to businesses or residences. CISPR 25 is more focused on the performance of radios and other receivers mounted in the vehicle as opposed to being a regulatory standard.
- ISO 11451 & ISO 11452: Both of these standards specify the test methods of road vehicles regardless of the engine type, whether it is gasoline, diesel, or electric, for narrowband radiated electromagnetic energy. ISO 11451 is targeted at testing the immunity of the vehicle to different disturbances, while ISO 11452 focuses on testing the immunity of the electronic components used in vehicles to various sources of interference.
- ISO 7637: This standard covers testing for electrical disturbances from conduction and coupling.
- ISO 10605: This standard specifies the testing for electronic modules in vehicles to disturbances from electrostatic discharge.
- SAE J1113: This is a series of standards that cover various electromagnetic compatibility measurement procedures as well as specifications for immunity to radiated interference.
These are a sampling of the standards that you may have to work with as you design your products to be EMI and EMC compliant.
Design Methods to Help Ensure Automotive EMI/EMC Compliance
In order to design circuit boards that will be compliant with all of the pertinent automotive standards, you will need to follow some basic PCB design for EMI and EMC methods. These will include making sure that you have good impedance matching and that you provide plenty of bypass capacitors and ground shielding. You will also want to make sure that you keep your routing short to minimize any chances of loops acting as an antenna and your current return paths clear. Obstacles in the ground plane, like cutouts, can increase the distance the current has to flow, which in turn could act like another antenna.
Another good idea is to work with a PCB contract manufacturer that will work with you on these EMI and EMC compliance requirements. At VSE we have worked with many customers on their specific EMC requirements, and we have a skilled staff of engineers and technicians that can provide the same level of expertise to you.