Automotive solutions have to meet strict requirements for Electro Magnetic Capability (EMC) and this is fundamentally a system integration issue. With the number of ECU’s and wire harnesses increasing in quantity and complexity, the issue is only likely to get worse. The challenge is not an increase of electronics but also the OEM time to market requires shorter times for validation in the final product. The pace of consumer electronics advancement also makes hardware redundancy more complex and puts pressure on making the cars systems to migrate faster to keep up with this pace.
One of the ways TI helps our customers is by understanding the process of integrations, the standards that govern the market, and also how our components play a part in this puzzle. Designers now have less time to validate our solutions and need more proof that power supplies do not exhibit interference in the system. The major OEM’s have their own standards for EMC and use these within the RFI’s when they are tendering their business to the Tier 1’s.
The CISPR 25 is the automotive standard for EMC issued by the International Electrotechnical Commission (IEC), which is widely adopted by many auto makers and OEM’s. In the CISPR 25, there are five classes of emission limits for the specified frequency bands, and Class 5 is the most stringent standard. The following table shows the CISPR 25 conducted emissions limits in Class 3 and 5.
Although there are many standards specified from the OEM’s, most are based on CISPR 25, and share the same test methods and only have some variants in the EMI limit levels.
To enable review of our devices before development, we created a Class 5 reference design to support the toughest specification of CISPR 25. The LM26001 is an AECQ qualified Wide Vin, DC/DC converter developed for Automotive applications and was used to develop the PMP9397 EMC reference design.
The PMP9397 reference design provides a conducted EMI optimized 3.3W power supply design for automotive applications like Cluster, Infotainment or Body systems. It uses the LM26001 non-synchronous buck regulator to generate a 3.3V, 1A output. The input voltage range of 4.5V to 38V is suitable for automotive battery supplies. The reference design comes with the input EMI filter stage to suppress switching noise in the input supply line and the board is tested to be compliant with the CISPR 25 Class 5 conducted emissions standard.
The PCB board can be seen in the above picture. Based on a 4 layer design, we are able to use compliance to the toughest CISPR 25 standard for conducted EMI. There’s an input conducted EMI filter section which must be considered in the overall solution cost to provide a realistic indication of total space requirements and additional costs.
The EMC plot on the left was taken from a sweep of frequencies 150 KHz to 30 MHz, and the plot on the right is for 30 MHz to 108 MHz which cover all major radio frequencies from AM band to FM band. The red linerepresents the averge detect limits of the CISPR 25 Class 5 standards, and the blue trace is the averge detection result compliant with the standards (below the limit lines). Peak detection (yellow trace) is below the correspondent peak limits, as well.
The design demonstrates that our technology is well-suited for Automotive applications and provides confidence to the engineer, PCB layout guidance, in addition toreducing design time and system integration. It can be used to validate component selection prior development which saves time and eliminates design re-spins to meet the OEM standards and accelerate time to market while saving R&D costs.
What challenges have you faced? Leave a comment and let me know.
- To download design files and schematics for the LM26001 CISPR 25 reference design, visit ti.com/tool/pmp9397
- To order samples and get additional design resources for LM26001, visit ti.com/product/lm26001
- To find more Wide VIN automotive design resources, visit the Wide VIN Automotive applications page at ti.com/widevin.