EMI Bites: Many ways to fail EMC tests, but common-mode currents are the top trap.
EMI Bites: Many ways to fail EMC tests, but common-mode currents are the top trap.
Why are common-mode currents such a major problem?
Because they radiate with devastating efficiency.
Just a few microamps can push you beyond EMC compliance limits defined by industry standards.
How do you mitigate these issues?
First, you need to understand their root causes—which is often easier said than done.
In most cases, common-mode currents stem from PCB layout problems that weren't properly addressed during design.
Here are the most critical offenders:
- Return current and signal reference discontinuities
- Impedance discontinuities
- Crosstalk
Some of these create immediate problems, while others require multiple failure modes before generating common-mode currents.
Regardless of the path, the result is the same: EMC test failures.
One immediate fix?
Make sure you have a return and reference plane next to each signal layer. Keep this plane continuous (no cuts, splits, or large gaps), and place it as close as possible to the adjacent signal layer in the stackup.
This will start solving many of these issues and is fairly inexpensive to implement.
Don't wait for test failures to address these issues—tackle them from the start of your PCB design process.
If you're unsure how to implement these best practices or still working to master EMI control fundamentals, we have limited spots remaining in our new EMI Control Academy.
You'll get access to comprehensive courses, training materials, resources, checklists, expert coaching, and everything needed to master EMI control and consistently pass EMC tests like a true specialist.
Join the other specialists here: https://bit.ly/EMI-Control-Academy
To electromagnetic enlightenment,
Dario