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Keywords: isolation, isolator, digital isolation, digital isolator, UL1577, IEC60747, VDE0884
APPLICATION NOTE 5993
UNDERSTANDING THE SAFETY
CERTIFICATION OF DIGITAL ISOLATORS
Abstract: This application note summarizes the international safety standards and certifications that apply to
digital isolators. Our example shows how to use a data sheet and the standards' specifications to determine
which digital isolator is optimal for an application.
Introduction
Digital isolators provide signal isolation and the level shifting required for the correct operation of many
circuits. Equally important, they insulate the user from electric shock. With basic human safety
considerations so pertinent here, these isolators must undergo extensive testing and certification to ensure
user safety. This article briefly summarizes the international safety standards and certifications that apply to
digital isolators. An example exercise using the MAX1493x family shows how an IC designer must use a
datasheet and the standard's specification tables to determine which digital isolator will be optimal for an
application.
Basics of International Safety Standards
The International Electrotechnical Commission (IEC) is the organization that publishes the international
standards for electrical safety. Regional specifications are handled by bodies such as the UL (U.S.A.), CSA
(Canada), VDE (Germany), and CNCA (China); actual testing and certifications are done by the UL, CSA,
VDE, and TUV in Germany, and CQC in China.
Safety standards can be separated into three broad categories: equipment standards, support standards,
and component certification standards. Developed over time in many geographic areas and across many
industries, safety certifications evolved into a plethora of standards. In recent years great progress has
been made toward harmonizing these standards. When you see multiple prefixes on a standard, it indicates
a harmonized standard that meets the requirements of those entities. For example, a mixed standard
identified as BS EN IEC meets the British Standards Institute (BS), European Norms (EN), and IEC. This
harmonization of standards is a very slow process but very much needed. Until this is achieved, component
suppliers will have to meet as many of the requirements as possible to be able to sell their devices
worldwide.
Equipment Standards
Equipment safety standards apply, as you would expect, to end equipment which is assembled from
multiple components. These standards cover a variety of safety concerns including insulation, pressurized
gasses, and the strength of electrical cords. The IEC 61010-1 (safety requirements for electrical equipment
for measurement, control, and laboratory use) is concerned with the transient voltages that equipment will
experience and the characteristics of the insulation used. This standard does not specifically address
isolators. In fact, neither the word "isolator" nor "isolation" is found anywhere in this IEC standard. It is,
nonetheless, relevant to isolators because it specifies both the transient voltage and the minimum creepage
and clearance distances for the insulation. The insulation of a marketed isolator must, therefore, be
compatible with these IEC requirements.
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