8/14

EMC GUIDELINES FOR MICROCONTROLLER-BASED APPLICATIONS

3.4 MEASURING EMC PERFORMANCES

EMC performances are measured according to two different aspects:

– Electromagnetic Emissions (EME),

– Electromagnetic Susceptibility (EMS).

The two aspects differ according to the method of measurement, the problems identified and

their solutions.

If an MCU application passes a susceptibility test, it does not mean that it will pass emissions

tests, regardless of the types of test performed. Therefore, both EMS and EME testing must

be carried out.

STMicroelectronics has designed specific EMC testing for its microcontroller components. A

short description of the approach developed by ST, which can also be applied to microcon-

troller applications, is given below:

STMicroelectronics EMC Testing

The method is derived from IEC (standards) and VDE/SAE specifications.

First, an EMC test board that reproduces the typical environment of the microcontroller in an

application is designed for each microcontroller. Then, to ensure reproducible tests, the pin

loading is standardized according to SAE 1751 specifications.

Table 3. EMC Testing

3.4.1 Emissions Tests

There are two types of EME tests; conducted and radiated. Conducted EME tests are more re-

producible because they do not overly depend on the PCB.

3.4.1.1 Radiated EME Tests

To isolate the component’s EMC behaviour, the board is designed according to SAE 1752

specifications.

The board is placed on a metallic box in order to mask all other components.

Performances are measured in a Faraday cage with the electromagnetic radiator placed at a

distance of 3 meters. The results are measured using a spectrum analyser.

Power digital

Typically 100 µF electrolytic

Typically 100 µF ceramic

Input

GND or 10-k

Ω pull-up resistor if no GND

Output

50 pF to GND

EI-directional

Configure as output 50 pF to GND