AN1714 datasheet(29/46 Pages) STMICROELECTRONICS

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AN1714

Demonstration board for ST7538Q

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2.5

Burst and surge protections

The environments encompassed by this application include residential, commercial and

light-industrial locations, both indoor and outdoor. For this reason a series of immunity

specification standards and tests have to be applied to the powerline application to simulate

the environment.

The requirements include EN610000-4-2, EN610000-4-3, EN610000-4-4, EN610000-4-5,

EN610000-4-6, EN610000-4-8, EN610000-4-11 and ENV50204. All these tests are listed in

the EN50065-2-1 document (part 7, immunity specifications).

These standards include surge tests, both common and differential mode (1 kV/0.5 kV,

Tr=1.2u sec) and fast transient burst tests (2kV, Tr=5n sec, Th=50n sec, repetition frequency

5 kHz).

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

respect to the high voltage tests. In fact an efficient coupling circuit with low insertion losses

consequently obtains a very low impedance path from the mains to the power circuit of the

devices that can destroy the internal power circuits of the ST7538Q.

For this reason is recommended to add some specific protection on the path that links the

ATOP pins to the mains.

Figure 26.

Common mode and differential mode spikes example

A solution that uses three transil diodes (P6KE6V8A or SM6T6V8A) connected in a star

configuration has been implemented in the demonstration board. A bidirectional transil was

not used because for common mode surge it is better to have a discharge path to ground

external to the devices.

In receiving mode the ATOP2 pin polarizes the coupling interface to ground. In this condition

without the diode D17 all the external signals greater than 1.4 V peak-to-peak are clamped

by D15 and D16.

In some conditions the transil diodes may not be reliable in presence of fast transient bursts.

In this case it is possible to add some fast response ESD diodes as ESDA6V1L (two

components) connected in parallel to the transil with the same star configuration.

The solution used for the demonstration board can give some general guidelines but can't

be generalized to all types of powerline communication applications.

Considerations about surge and burst protections depend on several factors such as

coupling interfaces, the board layout or the characteristics of the components used. Every

application needs a specific analysis.

1:1

ST7538

1:1

ST7538

Differential Mode

Common Mode

D16

D17

D15

D16

D17

1:1

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