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EMC DESIGN GUIDE FOR ST MICROCONTROLLERS

2.2.2 EMI level classification

The EMI classifications are directly based on the absolute frequency and amplitude of the

emitted noise. Several international norms exist, based on different measurement methodolo-

gies, or emission levels, but the classification principle remains the same.

The standardized diagram (see Figure 9.) is useful to get a synthesis and a classification of

EMI results, according to a standard framework. Each ST microcontroller EMI result is classi-

fied according to 4 SAE levels.

Figure 9. EMI level classification:

Below is the potential risk associated with each EMI level:

_ higher than 4. high risk due to EMI level.

_ Level 4. may require cost for EMI compliance.

_ Level 3. moderate EMI risk.

_ Level 2. minimal EMI risk.

Table 10 shows how EMI test results are presented in ST datasheets.

Table 10. Example of EMI results

for ST72F521

To give a synthetic view of the emission spectrum, the highest emission level of 3 ranges of

frequency is indicated. EMI data are provided with relevant information such as the device

package and CPU frequency.

dbu V

-20

0.1

100

1000

MHz

Level 4

Level 3

Level 2

Level 1

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