Avago Technologies ACPL-224-500E - Manual (Page 3)

AV02-4387EN 1 Avago Technologies
Insulation and Regulation of Optically Coupled Isolation Devices
Design Considerations
The primary purpose of opto coup ler
devices is to provide both electrical
insulation and signal isolation. The
popularity of Avago Technologies'
product offer ing can be accred-
ited to cost-effective innovations
in these areas. Yet there exists a
surpris ing level of misunderstand-
ing regarding these two terms from
both vendor and user alike. The
discrepancies that exist within the
worldwide regulatory community
add to the frustration level for many
designers. This discussion attempts
to help the designer capitalize on
Avago Technologies’ knowledge.
Insulation Defined
The electrical insulating capabil-
ity of an optocoupler, sometimes
referred to as withstand voltage, is
determined by its ability to protect
surrounding circuitry, as well as
itself, against physical damage re-
sulting from different voltage po-
tentials. This potentially damaging
phenomena can be system induced
(e.g., motor rail voltage) or externally
coupled (e.g., lightning pulse). The
insulating material between input
and output as well as the packag-
ing technology are the primary de-
terminants of withstand voltage ca-
pability. In contrast, signal isolation,
although sharing some common
causes, defines the ability of the op-
tocoupler to prevent the distortion
of data through the suppression and
filtration of common-mode tran-
sients. A further discussion of signal
isolation can be found in the section
entitled “Common-Mode Transient
Rejection.”
The effects of repeated long-term
high-voltage stress between input
and output of an optocoupler has
continued to be an area of uncer-
tainty. Much of the technical em-
phasis has been on the ability of
optocouplers to withstand one-time
short-term high-voltage transients
(e.g., U.L. 1 minute dielectric voltage
withstand rating). Avago Technolo-
gies has conducted extensive op-
erating life tests to determine the
effects of continuous high-voltage
stress, both transient as well as
steady-state, on the degradation of
insulating perfor mance. On comple-
tion, the test data was analyzed to
determine safe operating areas for
steady-state input-output high-volt-
age stress. The boundary conditions,
as shown in Figures 1, 2, 3, have been
defined by Avago as Endurance
Voltage. The lower region refers to
the safe operat ing area for the appli-
cation of continuous steady-state ac
and dc input-output voltage stress,
or working voltage, and the middle
region to transient voltage stress.
Operation above these regions has
shown to cause wear-out either in
functionality or insulat ing capabil-
ity and is not recom mended. En-
durance Voltage is based on the
inherent properties of Avago opto-
couplers that utilize unique packag-
ing technologies and does not apply
to products manufac tured by other
vendors. In addition, as these tests
do not take into consideration par-
ticular equipment use conditions,
Avago recommends the designer
consult the appropriate regulatory
agency guidelines to determine
applicable working voltage. For an
in-depth discussion on Endurance
Voltage, consult Avago Application
Note AN1074.
Regulatory Environment
Because electrical insulation is a
function of safety, optocoupler per-
formance, both at component and
system levels, is often subject to reg-
ulatory requirements and approv-
als that vary according to country
as well as industry. Most agencies
are a mixture of govern mental and
private organizations with industry
representation. Some common reg-
ulatory agencies are listed in Table 9.
Currently, little conformity exists be-
tween the various agencies regard-
ing mechanical configura tions and
electrical test require ments. Within
the European Union, however, stan-
dardization of equipment as well as
compo nent level specifications is in
progress. In the interim, testing and
approval according to equipment
type and environ mental factors
must be obtained according to the
control docu ments of each country.
The International Electrotechnical
Commission (IEC), with worldwide
representa tion, provides a forum for
generating technical standards. The
European Committee for Electro-
technical Standardization (CENEL-
EC), has European Commission
authority to adopt IEC standards
as European Norms (EN), with the
force of law.
Table 9. Common Regulatory Agencies
Name Country Abbreviation
Verband Deutscher Electrotechniker Germany VDE
Underwriters Laboratories United States UL
Canadian Standards Association Canada CSA