AN3181

Compliance with IEC and VDE standards

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7/31

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Compliance with IEC and VDE standards

The IEC (International Electrotechnical Commission) is a non-profit and non-governmental

authority recognized worldwide for preparing and publishing international standards for a

vast range of electrical, electronic and related technologies. IEC standards are focused

mainly on safety and performance, the environment, electrical energy efficiency and its

renewable capabilities. The IEC cooperates closely with ISO (International Organization for

Standardization) and ITU (International Telecommunication Union). Their standards define

not only the recommendations for hardware, but also for software solutions. Standards are

divided into a number of safety classes depending on the purpose of the application.

The other bodies that are recognized worldwide in the field of electronic standard

organizations are VDE in Germany, IET in the United Kingdom and the IEEE in the United

States. The VDE association also includes a Testing and Certification Institute which is a

pioneer of software safety inspection. This is a registered National Certification Body (NCB)

for Germany. The main purpose of this testing house is to offer standards compliance and

quality testing services to manufacturers of electrical appliances.

One of the pivotal IEC standards is the IEC 60335-1 norm, which covers safety and security

of household electronic appliances destined for domestic and similar environment.

Appliances incorporating electronic circuits are subject to component failure tests. The basic

principle is that the appliance must remain safe in the case of any component failure. The

microcontroller is an electronic component just like any other from this point of view. If safety

relies on an electronic component, it must remain safe after two consecutive faults. This

means the appliance must stay safe with one hardware failure and with the microcontroller

not operating (under reset or not operating properly).

If the safety depends on software, the software is taken into account with the second applied

failure. The conditions required for software are defined precisely in Annex Q of the

IEC 60335-1 norm. Three classes of appliances are defined here:

●

Class A: Safety does not rely on software

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Class B: Software prevents unsafe operation

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Class C: Software is intended to prevent special hazards

This application note and the associated ST software package covers the group B

specification. Appliances under group C need some other special requirements such as

dual microcontroller operation, which is outside the scope of this document.

Class B compliance aspects for microcontrollers are related both to hardware and software.

A list of microcontroller parts under compliance is evaluated at IEC 60335-1 Annex T which

refers to IEC 60730 Annex H. This list can be divided into two groups - micro-specific and

application-specific items. (see Table 2: MCU components to be tested for Class B

compliance).

While application-specific parts rely on customer application structure and must be defined

and developed by users (communication, I/O control, interrupts, analog inputs and outputs),

micro-specific parts are related purely to the micro structure and can be made generic (core

self-diagnostic, volatile and non-volatile memory integrity checking, clock system tests). This

group of micro-specific tests is the focus of the ST solution based on powerful hardware

features of STM8 MCU such as dual independent watchdogs or clock sources.

It is important to note that there are several other peer recognized bodies concerning

electronic safety standards besides IEC, such as VDE in Germany, IET in the United

Kingdom and the IEEE in the United States. In addition, an increasing number of product