App note: EMC guidelines for microcontroller-based applications


Application note(PDF) specific on microcontroller EMC from ST Microelectronics.

Electromagnetic compatibility (EMC) must be taken into account at the very beginning of a project as the cost of correcting an EMC problem encountered at the start of production can be far greater that the cost of a detailed EMC study during the development phase of an application.

The use of microcontroller-based systems is increasingly wide-spread, especially in such areas as consumer, industrial and automotive applications, where the drive for cost reduction is the common trend. This emphasis on cost reduction and the increasing complexity of such systems requires the manufacturers of semiconductor components to develop highly integrated, single chip, high operating frequency microcontrollers using the highest density technology possible. Unfortunately, for semiconductor structures, the higher the density and the faster the operation, intrinsically the higher the level of electrical noise generated, and the increased sensitivity to spikes induced from external noise. Therefore, the PCB layout, the software and the system must now apply EMC “hardening” techniques in their design.

This note aims to provide guidelines for designers of microcontroller-based applications so that the optimum level of EMC performances can be achieved.

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  1. The problem for makers is many of the tools we are using for development don’t meet these standards or approvals meaning that we can only make prototypes to prove concepts.
    To finalize a project for commercial sales still requires alot of knowledge on this subject which is beyond most of our abilities.

    Wouldn’t it juts be easier if the modules met these standards in the first place, after all they are commercially sold!

    1. The problem with the modular thinking is that even if a module itself might be compliant, but can still fail to pass when combined together with other modules. There can also be different acceptance criteria in various end applications. In the EU we have a household standard and another for office equipment. Both standards can reference towards an EMC standard, but depending on the application, different acceptance levels can apply. There can also be product type specific amendments that can tell you to “take the value from table X in standard Y and then add 30% safety margin on top of that”.

      So there is no easy way out. Just because all the modules are compliant themselves, the assembled product in the designated application might still fail to be compliant.

      1. In fact, if you are actually preparing a product for the market and need to do EMC testing (whether for FCC or European CE), you have to always test the entire product.

        Whether or not some Chinese module carries a CE mark is completely irrelevant – first, the mark can be fake or meaningless, with no actual testing done (for CE you self-declare compliance, you get in trouble only if someone actually “checks”, which nobody is going to do for a fly-by-night Chinese outfit).

        Second, as you said, there is no guarantee that even a certified module won’t interfere with something else when installed in a larger system. Typical case are power leads acting as antennas, chassis changing radiation patterns focusing the EMI in one direction where it will exceed the permitted limits, etc.

        For a hobbyist this is a non-issue, but one needs to be aware of this when preparing something for sale – lots of Kickstarters are not budgetting for EMC testing and many are very obviously not even aware that something like that is even required.

  2. I totally agree with Jan! Also don’t trust UL, TUV or VDE markings or certificates without double-check at their websites. It is common practice to “borrow” test certificates or extend a product range. If the 1uF X2 cap is listed, the 2.2uF might not be.

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