In his recent webinar, “Simple Ideas to Make EMI Issues a Thing of the Past”, David Bourner presented a useful checklist to help engineers ensure that they address EMI during the design process. The checklist items described below are a valuable tool to ensure that certification becomes a much less stressful time.
Design for EMI from the Beginning
It’s important to think about EMI from the start of the project. In particular engineers should know what performance is required and use this to drive their approach to development.
Select Components and Circuits with EMI in Mind
EMI should be one of the key criteria used to select components and modules. It’s important to remember that different components have very different EMI characteristics. For example, low-frequency, hard-switching converters are likely to generate much more interference than high-frequency, soft-switching alternatives. Choosing devices that generate lower emissions will make achieving certification much more straightforward.
Plan Your PCB Layout
The design of your PCB has a very significant impact on the EMI performance of the system. To minimize problems, it’s important to consider several factors. Firstly, the board stack-up should be optimized, with ground planes to be located close to matched power and signal trace layers. Components such as filters, SMPS modules and other critical analog or digital circuits should be placed first, as should return traces to minimize the trace length and EMI that is generated.
Determine Cable Harness Design
The design of cabling also impacts the EMI generated by an electronic system, so engineers should consider email when selecting and deciding where to place connectors.
Plan Grounding Strategy
Planning the grounding of a system is an important step to minimizing EMI. Designers should make sure they consider grounding at all levels: component, circuit, module, circuit card and system.
Select Filters Carefully
Filters are obviously key components to ensure EMI compliance so it is important to choose the right product for the design. Power developers should verify ratings, use correct components and make sure that they separate input & output routes.
Ensure Effective Shielding
When designing shielding, it’s important to consider the noise spectrum, and select materials that are appropriate for these frequencies. Designers should also look carefully for gaps (as a rule of thumb any gap larger than λ/20 is likely to cause a problem) and deploy conductive gaskets where needed.
Use the Schematic as a Tool to Document EMI Control Design
The schematic is a great tool to document the steps taken to mitigate EMI. Engineers should apply a flow check to ensure assignment of appropriate in-circuit control measures. The schematic is also a great place to check that the input filtering design is conducive to input power bus stability.
Carry out EMI Pre-Assessments Continuously
EMI is not something that can be left until final test and certification, unless you like nasty surprises! Testing should be conducted throughout the design process to ensure that any potential issues are identified, and remedied, as early as possible in the development cycle. This approach reduces the time and effort required to address problems, cutting risk and decreasing time to market.
“Simple Ideas to Make EMI Issues a Thing of the Past” is available as an on-demand webinar on the Vicor website. Click here to get more ideas from Dave Bourner that will help you eliminate EMI problems in your next design.