AN17

DESIGN IN G FOR IN TER NA TI ON AL SAFETY COMPL IA NC E

Introduction

This application note is a practical guide to obtaining

certification marks for safety compliance worldwide. The

information presented here is based on a successful

submittal of the Si3034PCI-EVB evaluation board to

Nemko Compliance West. The resulting CB Test Report

and Certificate for the Si3034PCI-EVB are available

upon request.

The information provided comes primarily from the web

sites of many Certification Agencies and from a UL-

sponsored seminar entitled “Information Technology &

Telecommunications Equipment: Designing for

Compliance to UL1950.” Also, working with Nemko

Compliance West, Inc. provided strong insight into the

Nordic Exclusions and other National Deviations.

CB Scheme

The Scheme of the IEEE for Mutual Recognition of Test

Certificates for Electrical Equipment is commonly known

as the CB Scheme. In the CB Scheme, a manufacturer

to obtains a CB Certificate for a given product. This CB

Certificate indicates that an NCB (National Certification

Body) has tested the product and found it to be in

conformance with the relevant standard. The relevant

standard for Telecommunications (IT) and Information

Technology (ITE) equipment, under the CB Scheme, is

the IEC 60950.

The process of obtaining a CB Certificate begins with

the submittal of product samples to a CB Test

Laboratory for evaluation. A CB test report is generated

based on the evaluation. If the CB test report indicates

that the product conforms to the applicable standard,

then a CB certificate is issued to formally declare the

product to be in conformance with the IEC 60950. The

CB test report is included as supporting documentation

to the CB certificate. If the product fails to conform to the

applicable standard, a special test report can be derived

from the test data, which can be useful in determining

areas that require improvement and/or redesign.

Obtaining a CB Test Report and Certificate does not

automatically mean the product has obtained the

Certification Marks required for approval in the desired

countries. The next step is to submit the CB Test Report

and certificate to the Certification Agencies for the

desired Certification Marks. The CE Marking is a

separate topic and will be discussed in a later section.

The procedure for submission to each Certification

Agency varies. Typically, a Certification Agency requires

a product sample and a completed Application Form in

addition to the CB Test Report and Certificate. As long

as the CB Test Report addresses all of the National

Deviations applicable to the countries to which the

Certification Marks applies, no additional testing is

required. Hence, it is important to let the CB Test

Laboratory know which countries the product targets so

that the applicable National Deviations are considered

in the generation of the CB Test Report and Certificate.

It is important to note, each Certification Agency has

differing requirements for maintaining the Certification

Mark applied to the product.

The CB Scheme, as it applies to IT and ITE equipment,

is fully accepted by the following Countries/Certification

Agencies:

Australia/SAA, Norway/NEMKO, Austria/OVE, Poland/

PCBC, Belgium/CEBEC, Canada/CSA, Singapore/PSB,

China/CCEE, Slovakia/EVPU, Czech Republic/EZU,

Slovenia/SIQ, Denmark/DEMKO, Finland/FIMKO,

Spain/AENOR, France/LCIE, Sweden/SEMKO,

Germany/TUVP-Service, Switzerland/SEV, Germany/

TUVR-Land, Germany/VDE, UK/BEAB, UK/BSI,

Hungary/MEEI, USA/USNC, India/STQC, USA/FMRC,

Ireland/NSAI, USA/ITS, Israel/SII, USA/MET, Italy/IMQ,

USA/TUVRHNA, Japan/IECEE-JP, USA/UL, Korea/

IECEE-KR, Netherlands/KEMA.

The number of CB Certificates issued is a consideration

in choosing a CB Test Laboratory. The top three

Agencies with the most number of CB Certificates

issued in 1998 for IEC 60950 (IT/ITE equipment) are

Norway/NEMKO (1395 submissions), Germany/TUVR-

Land (767 submissions), and USA/UL (694

submissions).

The relevant standard for Telecommunications (IT) and

Information Technology (ITE) equipment, under the CB

Scheme, is the IEC 60950. The current active version of

the IEC 60950 is the 2nd Edition, Amendments 1–4.

The IEC 60950 3rd Edition is expected to replace the

IEC 60950 2nd Edition by mid 1999.

Most of the requirements for Safety Compliance are

based on the IEC 60950. However, each country may

have requirements beyond IEC 60950. These

Preliminary Rev. 0.1 10/99 Copyright © 1999 by Silicon Laboratories AN17-01 This information applies to a product under development. Its characteristics and specifications are subject to change without notice.

AN17

2 Preliminary Rev. 0.1

differences, called National Deviations, are first covered

by CB Bulletins. These CB Bulletins are distributed

periodically to the NCBs and CB Testing Laboratories.

Many countries use the IEC 60950 document, plus CB

Bulletins as adequate specification for compliance.

Occasionally, there are enough differences to warrant a

separate standards document based on the IEC 60950.

An example is the UL1950 standard.

The EN 60950 is a CENELEC (Comité Européen de

Normalisation Electrotechnique) standard based on the

IEC 60950. It covers the National Deviations applicable

to the 18 member countries of the European Economic

Area, also known as the European Union (EU). The 18

member countries include the following: Austria,

Belgium, Denmark, Finland, France, Germany, Greece,

Iceland, Ireland, Italy, Liechtenstein, Luxembourg,

Netherlands, Norway, Portugal, Spain, Sweden and the

United Kingdom.

The UL1950 (3rd Edition)/CSA C22.2 No. 950-95 (Third

Edition) is a bi-national standard based on the IEC

60950. UL1950 applies to the United States and

Canada.

CE Marking

The CE Mark is a “passport” which permits a product’s

entry into the 18 member countries of the European

Economic Area. It is important to note that the CE

Marking is not a Certification Mark issued by a

Certification Agency under the CB Scheme.

The CE Marking, along with a Declaration of Conformity

and Technical File, is a manufacturer’s declaration that

the product complies with the directives applicable to

the product. The directives that apply to IT and ITE

equipment are as follows: Low Voltage Directive (LVD),

Electromagnetic Emissions Directive (EMC) and the

Machinery Directive (with moving parts).

Typically, a product is submitted to a Notified Body.

Notified Bodies are authorized by European countries to

serve as independent test labs and perform the steps

called out by product directives. They must have the

necessary qualifications to meet the testing

requirements set forth in the directives. Notified Bodies

may be private sector organizations or government

agencies. Manufacturers may choose a Notified Body in

any member state of the European Union.

The Low Voltage Directive (CE Marking Directive 73/23/

EEC as amended by 93/68/EEC) applies to product

safety related to electrically operated devices. The EN

60950 is used to show conformity to Annex I (Essential

Requirements) of the LVD.

With the CE Marking, the manufacturer is not subjected

to periodic visits from a Certification Agency, because

there is no Certification Agency. Depending on the

directive and the complexity of the product, it is possible

to perform ‘self-assessment’ and declare a product to

be in conformance to the applicable directives.

However, self-assessments are more likely to be

challenged.

If a product is challenged, and it is found that the

required documentation does not support the signed

Declaration of Conformity for the specific directives that

apply to the product, then the manufacturer may be

penalized through the legal system.

Safety-Related Web Sites

There are many helpful safety related websites on the

internet. Here are just a few:

http://www.cbscheme.org

http://www.aqas.com.au/cemark1.htm

http://www.aqas.com.au/eec.htm

http://www.nemko.no

http://www.ul.com

http://www.iec.ch

http://www.us.tuv.com/library/resources/index.html

http://www.csa-international.org/links/index.html

http://www.ce-mark.com/cefree.html

http://www.eurunion.org/infores/standard.htm

http://global.ihs.com/

Steps to Safety Compliance

A Professional Testing Agency is a privately or publicly

owned consultation company that can act in the

capacity of a CB Test Laboratory, an agent to an NCB,

an NCB, a CE Notified Body, an agent to a Certification

Agency, a safety consultant, as well as in other

capacities. The Professional Testing Agency is in the

business of providing services for compliance testing.

When looking for a Professional Testing Agency, a good

place to start is the list of Certification Agencies. Many

of these Certification Agencies are also CB Test

Laboratories, NCBs, and CE Notified Bodies.

The general steps in getting CE Marking, CB Test

Report and Certificate, and other Certification Marks are

as follows:

1. Product Development Engineering should assess

the product for safety-related issues. If UL1950

compliance is required, there are system-level

construction issues that need to be considered at

this time.

AN17

Preliminary Rev. 0.1 3

2. Assign a Compliance Test Engineer who is familiar

with your product to be tested. The Compliance Test

Engineer will work with the Professional Testing

Agencies. There may be more than one agency

involved, depending on the services provided by the

Testing Agency.

3. Select a Professional Testing Agency. The following

is a checklist for choosing a testing agency:

• Has Test Setups required for IEC 60950 electrical

testing

• Receives CB Bulletins on a regular basis

• Has Knowledge of National Deviations pertaining

to the countries you want to enter. At the very

least, must be familiar with EN 60950

• Has UL1950 3rd Edition Overvoltage Test Setup if

North America is included in the target countries

• Has a good understanding of how to achieve

UL1950 3rd Edition compliance

• Can act as an agent on your behalf, for submission

of CB Test Report and Certificate to obtain

Certification Marks required

• Has experience writing CB Test Reports and

Certificates for ITE/TE appliances.

• Has experience preparing Declaration of

Conformance and Test Files for CE Marking

4. Submit samples of your product to the chosen

Professional Testing Agency to do the actual

electrical test and measurement of creepage and

clearance. If UL 3rd Edition Overvoltage Testing is

involved, it is important to plan ahead as to the

number of overvoltage tests that will be done. The

overvoltage tests may render the product inoperable

after the tests.

5. The Professional Testing Agency writes the CB Test

Report when the product meets the requirements for

safety.

6. The Professional Testing Agency submits the CB

Test Report to the NCB to obtain the CB Certificate.

Typically, the first Certification Mark is obtained from

the NCB issuing the CB Certificate.

7. The CB Test Report can be used to show

conformance to the LVD Directive. The Professional

Testing Agency compiles the CE Test File, which

contains a copy of the CB Test Report.

8. The Professional Testing Agency compiles the

Declaration of Conformity for the LVD Directive. An

officer of the company will sign the Declaration of

Conformity for the LVD Directive. Assuming that the

other CE directives are met (e.g., EMC Directive),

and all documents are in order, then the product may

be shipped with the CE Marking.

9. Work with the Professional Testing Agency to submit

a sample of the product, CB Test Report and

Certificate, and Signed Application Forms (supplied

by Certification Agency) to other Certification

Agencies for obtaining their Certification Marks.

Design Considerations for Product Safety

This section discusses the treatment of the principles of

safety as it relates to the modem circuit. There are other

considerations of safety such as power supply issues,

and fire enclosures. Safety issues outside the scope of

the modem sub-system are best handled through

consultation with the Professional Testing Agency.

2.5-mm Isolation Barrier

In all modem designs, there is a portion of the modem

which is isolated from the local ground. These isolated

components are part of an IEC 60950 classification type

called the TNV-3 (Telecommunications Network Voltage)

Circuit. TNV-3 circuits are subject to ringing voltages

and lightning surges. TNV-3 circuits are not

considered safe to touch by the user.

Circuits powered by low-voltage DC supplies in which

no hazardous voltages are generated are called SELV

(Safety Extra Low Voltage) circuits. SELV circuits are

safe to touch by the user and include the local ground.

All components from Tip/Ring to the Si3014 (Line Side)

device are considered to be in the TNV-3 Circuit area.

The Si3021 (DSP-side) is considered to be on the SELV

Circuit area. Figure 1 shows the SELV and TNV areas.

AN17

4 Preliminary Rev. 0.1

Figure 1. Si3034 Modem Design Overview

The boundary between the TNV-3 and SELV Circuit

area is frequently called the Isolation Barrier. In an

Si3034 design, the Isolation Barrier is between the

Si3021 and Si3014. The IEC 60950 term for a

separation between the SELV and TNV-3 is the

application of “Insulation” between these two circuit

types.

There are many classifications for insulation between

the TNV-3 and SELV. The most common requirement is

that of “Basic Insulation”. “Basic Insulation” defines the

required distance across the Isolation barrier.

The separation between the TNV-3 and the SELV

portion of the circuit is also a function of the normal

working voltage expected between the TNV-3 and the

SELV, as well as the expected conductive dust

conditions that may accumulate on the Isolation Barrier.

For an international modem, under the worse case

conditions of ringing voltages and conductive dust

particle pollution, the required minimum distance is

2.5 mm. This 2.5 mm distance is to be applied from any

PCB trace between the TNV-3 area to SELV circuit and

from any PCB trace between TNV-3 and local ground.

This distance is measured by skimming the surface of

the PCB and is called “creepage” in IEC 60950

terminology. Creepage distance is applied to prevent

electrical arcing across conductors as a result of dust

particle accumulation over a surface. Dust particle

accumulation, over time, can degrade the isolation

between conductors. Distance through air, called

“clearance”, does not have this dust particle

accumulation problem. Hence, creepage distance is

always larger than clearance. In the case of TNV-3 to

SELV separation, the required minimum clearance is

2.0 mm. Since both clearance and creepage distance

requirements need to be met, the larger value of

creepage distance is used.

Figure 2 shows an example of creepage distance and

clearance.

TNV-3

Si3021 Si3014

Isolation Barrier C24

Dio

de

B

ridg

e

Dis

cre

tes

AN17

Preliminary Rev. 0.1 5

Conductor Conductor

Figure 2. Creepage vs. Clearance

TNV Cover

The IEC 60950 states that TNV-3 circuits must not be

accessible to a casual user. The casual user is referred

to as the “operator” in the IEC 60950. As mentioned

previously, TNV-3 circuits are not considered touchable

by operators. In the example of a PCI Modem inside a

personal computer (PC), some countries consider

operating a PC without the enclosure as a normal

operating environment. As such, these countries will

require a cover around the TNV-3 area.

The TNV cover is intended to prevent an operator from

touching live TNV-3 circuits when the PC is used

without its primary enclosure. If the cover is made of

plastic, then there are no distance requirements

between any exposed TNV-3 conductor and the plastic

cover.

If the cover is made of a conductive material, then the

minimum distance of 2.5 mm “creepage” applies to the

base of the metallic TNV cover and any TNV-3 trace.

This 2.5 mm creepage distance is measured along the

surface of the PCB.

As indicated previously, the air-distance called

“clearance” is required to be 2.0 mm, not 2.5 mm.

Hence, the height of a metallic TNV cover is determined

by the tallest conductive component on the TNV-3

Circuit area plus 2.0 mm.

To build an international modem, it is best to make

provisions for the TNV Cover. But for cost purposes,

ship the TNV cover only to countries that require them.

The Professional Testing Agency should be

knowledgeable as to which countries require a TNV

cover.

For instance, North America does not require the TNV

cover as long as the documentation warns the user or

operator to unplug the phone cord while installing the

modem.

Isolation Barrier Capacitors

In many designs, including the Si3034PCI-EVB,

capacitors are used to bridge the Isolation Barrier. For

the Si3034PCI-EVB, these are C1, C2, C4, C24, and

C25. The IEC 60950 requires that this Isolation Barrier

be suitable for “Basic Insulation”. Figure 1 shows an

overview of how the isolation capacitors are used.

Essentially, a capacitor that is able to reach across the

2.5 mm Isolation Barrier is considered to be “Basic

Insulation.” Conceptually, a capacitor is constructed so

that two metal plates are separated by a suitable

dielectric material. The dielectric acts as an insulator

between the two metal plates. As long as the capacitor

is able to withstand the “Dielectric Strength Tests,” it

qualifies as “Basic Insulation.” In the process of having

your product tested, the capacitors will be subjected to

these electrical tests. High voltage capacitors (2000 V)

and Y2-class capacitors are able to withstand these

tests.

When submitting the product for testing, it is

recommended that alternate sources for the Isolation

Barrier capacitors be identified and tested. Not doing so

may result in the need for re-testing and re-qualification

of the system if a capacitor supplier is unable to meet

delivery.

Another item to consider are the footnotes in the IEC

60950 that require the isolation be upgraded to

“Supplementary Insulation” for Nordic Countries. These

footnotes are referred to as the “Nordic Exclusions”.

The Nordic Countries are Norway, Sweden, Finland and

Denmark.

Clearance

Creepage Distance

AN17

6 Preliminary Rev. 0.1

“Supplementary Insulation” has all the requirements of

“Basic Insulation.” In addition, the thickness of the

dielectric material between the poles of the capacitor is

governed by a “Minimum Distance Through Insulation”

of 0.4 mm. Figure 3 illustrates “distance through

insulation.”

Insulator or Dielectric

Conductor Conductor

“Distance through Insulation”

Figure 3. Distance through Insulation

Given this design constraint, the capacitor becomes

physically larger. The IEC384-14 is the standard that

governs the construction and the certification of a

capacitor suitable for applications that can be used to

bridge “Supplementary Insulation.” The capacitor suited

for “Supplementary Insulation” is defined as a Y2

capacitor. Besides the minimum distance through

insulation, a further design constraint of the Y2

capacitor is a 4-mm creepage distance between

opposite poles of the capacitor. This design constraint

requires a surface mount capacitor to be of size EIA

22xx or larger.

For applications that do not have significant height

constraints, it is recommended that ceramic disk

packaging be used in lieu of a surface mount. The

ceramic disk packaging requires two holes separated by

7.5 mm. There are many manufacturers who build Y2

capacitors that use the same 7.5 mm footprint. Among

them are Panasonic, Murata, and Samsung. An

inexpensive solution is to use all through-hole.

A surface mount Y2 capacitor of size EIA 2220 is

manufactured by Murata. Another option is to create

dual footprint pad sites that can host either an EIA 2220

or an EIA 1808 capacitor. The resulting pad sites are “T”

shaped. This way Y2 capacitors are used only for the

Nordic countries and standard EIA 1808 capacitors for

the rest of the world.

UL1950 3rd Edition Overview

The UL1950 3rd Edition overvoltage tests are required

only for the United States and Canada. After April 1,

2000, new product submissions need to be evaluated

against the UL1950 3rd Edition. Existing products that

were evaluated using other standards do not need to be

reevaluated until April 1, 2005. These overvoltage tests

is due to the co-location of phone lines and power lines

on the same utility pole network. In the event of a

failure, such as a tree falling over utility lines, it is

possible that the lines could cross, sending hazardous

voltages across the phone line. This is not the case in

Europe because the phone lines and power lines are on

separate utility poles, or the utility lines are buried.

The UL1950 3rd Edition overvoltage tests are defined in

Subclause 6.6 and Annex NAC. While designing your

product, it is important to obtain copies of the relevant

standards for your reference.

Assuming that the system is subjected to overvoltage

tests, voltage is applied to the system as a “differential

mode” or a “common mode.” For the “differential” mode,

also known as “metallic,” voltage is applied between Tip

and Ring, while other accessible conductors are

grounded. For the “common mode” tests, Tip and Ring

are tied together, and all other conductors are tied to

ground. A voltage is then applied to both Tip and Ring.

Another item of consideration is whether or not the

modem is placed “on-hook” or “off-hook.” For the

Si3034-based design, the loop current is actively

controlled through Q3. However this can be controlled

only when the system is powered on. When the system

is powered off, the system is always on-hook.

During safety testing, the system is not powered on. To

simulate an off-hook condition, the emitter and collector

of Q3 are shorted together. This shorting of the collector

and emitter of Q3 represents an artificial worse case

condition that will not happen in a real system. If the

system were powered on as it needs to be to go off

hook, excessive loop currents would be detected and

the system would be placed in the on-hook position

before any damage could be inflicted on the modem.

Even with the artificial condition of a shorted Q3, the

submitted Si3034-based design passed. Figure 4

shows the devices most affected by the off-hook

condition.

AN17

Preliminary Rev. 0.1 7

U2

Q1

Si3014

D1 FB1

2.2 A

Tip

+

Q2

Z1 FB2

200 V, RV1 not clamped, fuse

not blown, Q3 VCE shorted

–

Ring

D2 2.2 A

Q3 CE Short

Figure 4. Devices Most Affected by Overvoltages and Overcurrents, Off-Hook Case

In all of the overvoltage tests, two layers of cheesecloth

are tightly wrapped around the system, or sub-

assembly. To pass the tests, the cheesecloth must not

ignite. The key concept to remember is that the

manufacturer has the choice of where the cheesecloth

is applied by defining the assembly, or sub-assembly.

For instance, for a PCI Modem, it is possible to test the

PCI Modem sub-assembly separate from the PC. If the

PCI Modem sub-assembly is tested outside the PC

system, the cheesecloth is wrapped around the PCI

modem sub-assembly. The PC manufacturer may

choose to test the entire PC system with the modem

already installed. It is up to the manufacturer to define

the boundary of the system. The goal is to show

compliance to the UL1950 standard. It will be shown

later how overvoltage testing can be minimized.

To pass the overvoltage tests, the cheesecloth around

the system or sub-assembly should not ignite or char.

After each of the overvoltage tests, the system is

subject to a dielectric strength test to ensure that the

Isolation Barrier is intact. UL1950 3rd Edition defines

five overvoltage tests.

Test 1 and Test 5 are not discussed. It will be shown

later that it is simple to find a way of bypassing Test 1. It

will also be shown later that Test 5 is usually

unnecessary.

Test 2 subjects the system to 600 V at 7 A for

5 seconds. It is important to note that this is the only test

conducted that has a maximum current of 7 A

(assuming Test 1 is omitted).

Test 3 subjects the system to 600 V at 2.2 A for

30 minutes. An additional test, Test 3a, is done only if

an open circuit results from Test 3. For Test 3a, the fuse

is shorted and the system is subjected to 600 V at 135% of

the fuse rating for 30 minutes.

Test 4 subjects the system to a voltage just below the

tripping voltage of a voltage protection device

(Sidactor). For example, 200 V at 2.2 A for 30 minutes.

When overvoltage tests are performed, a passing mark

means the cheesecloth did not char or catch fire, the

wiring simulator did not open (test 1 and 5 only), and the

dielectric strength test (conducted after each

overvoltage test) shows the isolation barrier is not

damaged.

Minimizing UL 3rd Edition Overvoltage Tests

This application note presents Table 18b of the UL1950

specification in a slightly different way. This method of

presentation is designed to highlight the effect of system

elements on the required overvoltage tests. Table 1

shows a simplified matrix to determine if Overvoltage

Tests 1 and 5 are required. Test 1 and the requirement

of 26 AWG wire are directly linked. Test 5 and the

requirement of passing Subclause 6.3.3 of the IEC

60950 is directly linked. Subclause 6.3.3 defines the

requirements for separation of the telecommunications

network from earth ground.

It is important to remember that the goal of the

overvoltage tests is to reduce the risk of fire. As such,

there are non-electrical system elements such as fire

enclosures and spacings to consider.

In most cases, the system will not have to be subjected

to Test 1. To remove the requirement for Test 1, there

must be a warning in the documentation or on the

product. An example is shown below:

CAUTION -- To reduce the risk of fire, use only No. 26 AWG

or larger telecommunication line cord.

AN17

8 Preliminary Rev. 0.1

Another method of skipping Test 1 is to supply a phone

cord (AWG 26) with the product, as well as sufficient

instructions to indicate that the product must be used

with the enclosed phone cord, or an equivalent phone

cord, to reduce the risk of fire.

The manufacturer only needs to guarantee that the wire

from the modem to the phone jack on the wall uses 26

AWG cord. The wire within the building is not included in

the safety assessment because it is the builder’s

responsibility to use 26 AWG phone wires throughout

the building.

Table 1. System Element vs. Overvoltage Tests

Table 2. System Element vs. Overvoltage Tests

Test 5 can be skipped if the product complies with the

testing of Subclause 6.3.3 of the IEC 60950. In the

process of performing the tests for compliance to the

IEC 60950, this is already done. If for some reason it

has not been done, then the system is subjected to a

125 V test.

Table 2 shows the remaining overvoltage test (Tests 2,

3, 3A, and 4) required for different system configuration.

If a fuse is used, the fuse must be 100 A2-s limiting and

have a 1.3 A maximum steady state current. Typically, a

fuse or PTC manufacturer will state in their literature

that the product is compliant with UL1950/UL1459

power cross tests. Surface mount fuses are available. In

choosing a fuse or PTC, consult with a UL engineer to

ensure that it is suitable for this application.

A fire enclosure is used to prevent the spread of a fire

originating from the equipment. The precise

characteristics that make a fire enclosure are beyond

the scope of this paper. The important thing to

remember is that the system element of a fire enclosure

is key to eliminating the overvoltage tests. A good

example for a fire enclosure is a PC Chassis.

The system element ‘spacing’ on Table 2 refers to an air

distance of 25 mm between the TNV-3 circuit and

materials of flammability V-2 or worse. No spacing is

required if the TNV-3 circuit is next to materials of class

V-1 or better. In addition, if the TNV-3 circuit is adjacent

to an opening on the fire enclosure, then there are

restrictions to the size of the openings on the enclosure.

If the material adjacent to the TNV-3 circuit is unknown

or unspecified, it is assumed to be of flammability V-2 or

worse.

Table 2 illustrates that it is possible to skip all of the

overvoltage tests under certain conditions. It also shows

that inclusion of a fuse in the system has limited value.

A fuse without a fire enclosure makes it possible to skip

Test 2. But, since Tests 3 and Tests 4 are required

anyway, it may make sense to simply not have a fuse

and subject the system to Tests 2, 3 and 4. The only

value in skipping Test 2 is that Test 2 is a 7 A test, while

the other tests are 2.2 A tests.

System Elements

Overvoltage

Tests

Fuse

Fire

Enclosure

Spacing

Test 2

Test 3,

3a, 4

No No Don’t

Care

Required Required

Yes No Don’t

Care

Skip Required

No Yes No Required Required

No Yes Yes Skip Skip

Yes Yes Don’t

Care

Skip Skip

System Element

OverVoltage

Tests

26 AWG Test 1

No Required

Yes Skip

System Element

OverVoltage

Tests

Pass 6.3.3 Test 5

No Required

Yes Skip

AN17

Preliminary Rev. 0.1 9

A fuse in a system with a fire enclosure, provides a

slight advantage by eliminating the requirement of

spacing between the TNV-3 circuit and adjacent

materials.

A PCI Modem being tested by a PC manufacturer is a

good example. A PCI Modem is mounted into a PCI

slot. Perhaps the card is facing the rear of a Video Card.

As long as there are no tall components mounted on the

rear of the Video Card, then the minimum spacing of

25 mm is met simply because the PCI slots are

separated by slightly more than 25 mm by design. The

PC chassis is considered a fire enclosure. Assuming

that the user instructions include directions that indicate

the phone cord must be of 26 AWG or better, no

overvoltage tests are needed. If the phone cord of 26

AWG is supplied, the system will not require

overvoltage tests.

Consider the scenario in which this system is subjected

to an actual power cross.

The cord from the wall to the PC will not overheat and

present a fire hazard because the phone cord is 26

AWG or better.

The worse case scenario is that the PCI modem ignites.

If the PCI modem ignites, it is separated from the video

card by 25 mm. At the very worst, it will expel carbon

debris to the back of the video card. The PC chassis

being a fire enclosure, provides another level of

protection.

Consequently, the sample system above passes the

requirements of UL1950 without subjecting the system

to overvoltage tests or adding a fuse. The system

passes the UL1950 3rd Edition simply by

documentation and fire enclosure construction.

In the case of a PCMCIA modem, the modem is

assumed to be enclosed in a small metal enclosure. If

the PCMCIA card enclosure is designed with V-1

material around the TNV-3 circuit, then no overvoltage

testing or fuse is required.

Now consider a laptop with an integrated modem on the

motherboard. Depending on the enclosure material

used, the laptop may not be considered a fire enclosure.

In this case, a metal enclosure around the TNV-3 circuit

may need to be designed so that overvoltage testing

can be bypassed. Another option is to omit any fire

enclosure and subject the laptop to overvoltage testing.

Submission of the Si3034PCI-EVB

In picking a CB Test Laboratory, the manufacturer

needs to take into consideration existing relationships,

the cost of the tests, certification programs available,

location of the test facility, and many other factors.

The Si3034PCI-EVB has an official CB Test Report and

Certificate. The system was subjected to all of the

required tests for the IEC 60950 and all of the known

National Deviations, including those of North America.

The Isolation capacitors easily passed electrical testing.

The tests included the required impulse testing, followed

by dielectric strength tests, and finally insulation

resistance measurements. The Si3034PCI- EVB was

submitted with many different capacitor configurations

and with multiple sources (Venkel and Novacap). All

configurations passed.

There are many options available for compliance to the

UL1950. As mentioned earlier, construction of the

system has a large effect on the number and severity of

the overvoltage tests required.

No assumptions were made as to whether or not a fire

enclosure existed and the Si3034PCI-EVB was tested

at the sub-assembly level with the cheesecloth wrapped

tightly around the sub-assembly.

The Si3034PCI-EVB passes all overcurrent and over-

voltage tests for UL1950 3rd Edition compliance with

minor circuit modifications.

Figure 5 shows the designs that can pass the UL1950

overvoltage tests, as well as electromagnetic

emissions. The top schematic of Figure 5 shows the

configuration in which the ferrite beads (FB1, FB2) are

on the unprotected side of the sidactor (RV1). For this

configuration, the current rating of the ferrite beads

needs to be 6 A. However, the higher current ferrite

beads are less effective in reducing electromagnetic

emissions, thus requiring the capacitors (C24, C25) to

pass electromagnetic emissions.

The bottom schematic of Figure 5 shows the

configuration in which the ferrite beads (FB1, FB2) are

on the protected side of the sidactor (RV1). For this

design, the ferrite beads can be rated at 200 mA. It is

possible to use higher impedance ferrite beads without

requiring C24 and C25 to aid in passing

electromagnetic emissions.

Conclusion

It is important to remember that compliance to UL1950

does not always require overvoltage tests. It is best to

plan ahead and know which overvoltage tests will apply

to your system. System-level elements in the

construction need to be considered during the design

stages. Consult with your Professional Testing Agency

during the design of the product to determine which

tests apply to your system.

AN17

10 Preliminary Rev. 0.1

75 @ 100 MHz, 6 A

1.25 A FB1

Ti

RV1 75 @ 100 MHz, 6 A

FB2

Note: In this configuration, C24 and C25 are used for emissions testing.

C24

p

ing

1000 @ 100 MHz, 200 mA

FB1 1.25 A

Tip

Ring

Figure 5. Circuits that Pass all UL1950 Overvoltage Tests

1000 @ 100 MHz, 200 mA RV1

FB2

AN17

Preliminary 11

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DisclaimerSilicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. Silicon Laboratories shall have no liability for the consequences of use of the information supplied herein. This document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. The products are not designed or authorized to be used within any Life Support System without the specific written consent of Silicon Laboratories. A "Life Support System" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. Silicon Laboratories products are not designed or authorized for military applications. Silicon Laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons.

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