AN4068 datasheet(41/63 Pages) STMICROELECTRONICS

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AN4068

Reference design standard tests

Doc ID 022923 Rev 2

41/63

Possible environments for this kind of application can be both indoor and outdoor:

residential, commercial and light-industrial locations. To verify the immunity of the system to

environmental electrical phenomena, a series of immunity specification standards and tests

must be applied to the power line application.

The immunity requirements for any PLC metering application, communicating in the

European A band (9-95 kHz), are listed in the EN50065-2-3 document, which refers to

EN61000 and ENV50204 for the tests to be applied [5].

These standards include surge tests, both common mode and differential mode (+/- 4 kV

peak, tR = 1.2 µs, tN = 50 µs) and fast transient (burst) tests (+/- 2 kV peak, tR = 5 ns, tH = 50

ns, repetition frequency 5 kHz).

For the application to be able to withstand such a severe electrical overstress, the line

coupling capacitor C4 must be an X1 or Y2 type part, rated for 4 kV or higher pulses.

In the case of non-metering applications, communicating outside the A band, the

requirements are listed in the EN50065-2-1 document, which sets lower pulse levels.

In addition to the line coupling capacitor, safety and robustness of the application are

guaranteed by protection devices included in the board design, such as input varistor (MOV)

and protection diodes. The effect of the protection diodes is described below.

Figure 31 and 32 show the protection against common mode disturbances. The low-drop

Schottky diodes D2 and D3 are able to quickly absorb fast transient disturbances exceeding

the supply rails.

Figure 31.

Common mode disturbance protection - positive disturbance

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