AN4444 datasheet(47/68 Pages) STMICROELECTRONICS

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AN4444

Reference design standard tests

9.3

EMI immunity tests

The specific structure of the coupling interface circuit of the application is a weak point

against high voltage disturbances that can come from the external environment. In fact an

efficient coupling circuit with low insertion losses realizes consequently a low impedance

path from the mains to the power line interface of the device.

For this reason it is recommended to add some specific protections on the mains coupling

path, to prevent high energy disturbances coming from the mains from damaging the

internal power circuitry of the ST7590.

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 standard 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 the

EN61000 and ENV50204 for tests to be applied (see Part 2 - 3 of Section 14: Normative

references on page 63).

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 C5 must be an X1 or Y2 type part, rated for 4 kV or higher pulses.

In 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.

Beside the line coupling capacitor, safety and robustness of the application are guaranteed

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

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

Figure 38 and Figure 39 show the protection against common mode disturbances. The low-

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

exceeding the supply rails.

AN4444 Datasheet(PDF) 47 Page - STMicroelectronics