Standards, Agencies and Certification

■ Electrical safety standards
A safety standard is a document that specifies the requirements that a system or component must meet to provide a desired level of protection. For example, IEC-62368 is the safety standard for most consumer electronic devices and is considered a broad standard that covers the requirements of many other standards, and many certified current sensors comply with this standard. IEC-62368 replaces IEC-60950 for information systems and IEC-60065 for audio/video systems.

■ Certification body
Certification bodies create safety standards. The International Electrotechnical Commission (IEC) creates international standards, while other bodies create regional standards based on IEC standards and their own country needs. For example, UL (Underwriters Laboratories, USA), VDE (German Electrical Engineers Association), and CCC (China Compulsory Certification) created UL-62368, EN-62368, and GB-4943.1, respectively.

■ Certification agency
Certification agents issue certificates of conformity to standards. These may be the certification bodies mentioned above or accredited third-party testing laboratories such as TUV, CSA or BSA. The IEC develops standards but does not provide certification.

■ Safety certification
Safety certification is an assurance by an agency or organization that a system or component meets the requirements of a safety standard. This is accomplished by testing the product against the standard and by conducting factory inspections to ensure the product continues to be manufactured the same way it was when tested.

■ CB Certification
An IEC Notified Body Report (CB Scheme) is a series of tests performed on a component or system to ensure that it meets the certification requirements of all other notified bodies worldwide that participate in the scheme. This test combined with a regional certification ensures applicability worldwide, as each regional notified body (e.g. UL, VDE, CCC) applies amendments or their own requirements in addition to the requirements of the IEC standard. Generally, CB certificates cover worldwide requirements and are the ones Allegro provides on its website.

Insulation rating

■ Safety-related insulation
Safety compliant isolation must be provided between people and voltages above 71V _RMS or 120V _DC, including basic, supplementary and reinforced insulation mechanisms and components.

■ Galvanic isolation
Galvanic isolation means that the metallic parts of two systems are separated from each other. The insulating materials used to achieve isolation can include air, plastic, glass, or other dielectrics.

Basic/single insulation

■ Basic insulation
Basic insulation is used in combination with additional redundant insulation schemes to create a robust double insulation scheme. In some cases, basic insulation alone is sufficient if another insulation system is already present. Basic insulation can tolerate failure (insulation shorting) but the system should be safe. On the other hand, the combination of two basic systems may not meet the requirements for double insulation. Care should be taken when determining the final system architecture. The LC and LH packages are examples of Allegro packages with basic insulation (see Figure 1). For a more extensive list of Allegro packages and devices, see the Allegro website.

Figure 1: Allegro package with basic insulation. Courtesy of Allegro MicroSystems.

■ Single protection
Basic insulation and single protection provide similar levels of protection from hazardous voltages. Basic insulation and single protection are not the same as they are used in two fundamentally different standard systems. Basic insulation is a term used in the IEC standard system and means creating double insulation in IEC certified systems. Single insulation is a term used in the UL standard system and means that insulation is adequate up to a working voltage of 600V _RMS, which is sufficient for most systems.

Reinforced/double insulation

Whenever personnel must come into contact with systems involving hazardous voltages, including electrical power transmission and distribution, the system must have double insulation. Double insulation may consist of a single layer of reinforced insulation or multiple layers of other grades. Exceptions are made for trained personnel.

■ Double insulation
Double insulation is the application of a double redundant insulation mechanism to the basic insulation mechanism. Double insulation is a general requirement for ensuring personnel safety and is a concept of IEC standards.

■ Reinforced insulation
Reinforced insulation is a single insulation mechanism that has been tested to provide the same level of protection as double insulation. Reinforced insulation is used in many components where it is not practical to create two layers of insulation with two separate components. LZ, MA and MC are examples of Allegro packages with reinforced insulation (see Figure 2). For a more extensive list of Allegro packages and devices, see the Allegro website.

Figure 2: Allegro package with reinforced insulation. *Courtesy of Allegro MicroSystems.

■ UL double protection
This is a strict requirement for a narrow range of audio and video equipment up to 250V _RMS in the United States, and does not generally apply to other equipment.

Mechanical properties

■Creepage distance (D _CR)
Creepage refers to the minimum distance along the package surface between the IP loop and any other pin. This path does not count surface features less than a certain size (1mm for pollution degree 2) nor does it include any unconnected metal that could short the distance. The shortest distance from the sensor input to the output is usually at the edge of the package, and the shortest path must cross and clear metal pieces used in manufacturing called tie bars (see Figure 3).

Figure 3: Creepage path in a JEDEC package. *Courtesy of Allegro MicroSystems

■Clearance distance (D _CL)
Clearance refers to the minimum distance in air between the IP loop and the I/O and power terminals (see Figure 4). It may or may not be line of sight, since electrostatic discharges and sparks can go around corners. This means it may or may not be the same path as creepage, and for JEDEC packages, it is usually the same path. Clearance is used to determine the maximum voltage that can be applied to the body of the part, and indicates how far the part can go before the air breaks down and a spark can occur. Generally, the maximum voltage in an application is determined by the overvoltage category, so clearance limits the overvoltage of the part.

Figure 4: JEDEC Package Clearance Paths (Courtesy of Allegro MicroSystems)

■ Distance Through Insulation(DTI)
DTI refers to the minimum distance of the internal insulation between the IP loop and the die (see Figure 5). Standards require either a minimum DTI or additional testing to ensure the insulation system is adequate for its rating. Allegro current sensor insulation undergoes extensive high voltage testing to meet the requirements.

Figure 5: Distance Through Insulation (DTI) *Courtesy of Allegro MicroSystems

■ Comparative Tracking Index (CTI)/Materials Group
CTI is a measure of a material's resistance to the formation of conductive carbon tracking and erosion depth due to constant electrolysis. The test involves applying a drop of nitric acid to the material, applying a voltage through electrodes placed on the material, and measuring the etch depth of the surface upon completion. An etch depth of less than 0.1mm passes the CTI voltage level (see Table 1). Many of Allegro's IC packages are manufactured in Material Group II. We use mold compound.

■ Degree of dirt
Contamination in insulation refers to the degree to which conductive material accumulates on the component surface. Conductive contamination accelerates the formation of carbon tracking by concentrating the electric field along the surface. The more contamination there is, the more creepage distance is required for the same operating voltage. Contamination is characterized by degree, with 1 being the cleanest and 3 being the most polluted (see Table 2). Most electronic equipment enclosures are expected to have a pollution degree of 2. One way to reduce contamination is to add a conformal coating to the board to prevent the accumulation of conductive material on the surface of the package.

This allows the application to move to Pollution Degree 1 in polluted environments, allowing smaller creepage distances (or smaller devices) to be used, but please note that conformal coating is not considered insulation and does not affect required clearances.

Voltage Levels

■ Working voltage of basic insulation (V _WVBI)
The working voltage of basic insulation is the voltage at which the part is designed to withstand a specific period of time (typically 1000V) according to the manufacturer and the certification body. 20 This is the voltage at which the device can operate for 1000mV (or more than 200mV) without dangerous insulation degradation. This is usually met by requiring a certain package creepage distance according to a table in the specification. The working voltage is limited by the degree of pollution of the environment and the characteristics of the device surface (material group). A clean environment and a resistant protective layer (such as a conformal coating) allows higher voltages to be tolerated for the same creepage distance. Allegro current sensors use thin film materials internally and are designed and tested to exceed the working voltages limited by creepage distances.

■ Working voltage of reinforced insulation (V _WVRI)
Reinforced insulation is a single insulation equivalent to double insulation. The permissible working voltage of reinforced insulation is half that of basic insulation.

■ Operating voltage waveform
In the standard, the voltage AC Since we assume that it is available from the transmission line, the operating voltage is AC _RMS Depending on the system, the operating voltage may vary. DC to high frequency square waves. 30kHz Starting at , there are recommended derating values when using insulation above this frequency (IEC60664-4 (See Chapter 1, “Configuring Cisco IOS XE 1000 Series Routers.”) DC is because charges do not move much on the surface or inside solid insulators. AC is likely to cause less damage than DC The ratings are usually AC This is considered the peak operating voltage.

■ Operating voltage (V _IORM and V _IOWM)
The voltage across the insulation can be considered to be any waveform, anything that repeats is considered to be the working voltage. This makes it difficult to give a clear picture of what the working voltage is, and the standards take into account both sinusoidal and non-sinusoidal waveforms. For sinusoidal waveforms, such as power line voltages, the working voltage is a sinusoidal fraction. RMS The value (V _IOWM, the operating voltage of the transmission line input and output. Other waveforms are square waves, DC voltage, or any waveform, so the only parameter to consider is the peak voltage (V _IORM, the repetitive operating voltages at the input and output of the transmission line. When certification agencies test these voltages, they usually use pure sine waves, V _IOWM and V _IORM The rating is √2 are related by a coefficient of

■ Dielectric strength (V _ISO)
Dielectric strength 1 This is the minimum voltage that guarantees that the insulation of the package will not break down when applied for minutes. AC _RMS The test voltage is specified as a pure sine wave. 2 It contains two important pieces of information:

1. The insulation will not break down due to partial discharge for 1 minute.
2. The peak of the sine wave will not break down the insulation. The peak of the sine wave is longer than the peak voltage of the impulse test and is therefore considered a more generous indication of the peak voltage.

V _ISO applies to designs that experience transmission line transients that occur as temporary overvoltages. Temporary overvoltages are caused by interference with the power entering a building. This includes dropping a high voltage line across a low voltage line during service.

■ Impulse withstand voltage (V _IMPULSE)
Impulse withstand voltage is a measure of the maximum voltage a component can withstand when subjected to a lightning surge pulse. Impulse withstand voltage applies to systems connected to the power grid. In most cases, 1 Sine wave overvoltage rating for minutes (V _ISO The impulse is usually defined as the peak of the current, but may be higher. 1.2 × 50µs The device typically uses a pulse of 1 Minute peak pressure 1.3 It can withstand voltages up to twice the normal voltage. This is not generally specified in the certification, but the peak overvoltage is specified with a margin. This is the main indicator for setting the creepage distance of the power grid of the system.

■ Partial discharge
Partial discharge is a wear mechanism that occurs when there is an interface between materials with high and low breakdown voltages. For example, when a mold compound and a polyimide are bonded together and the insulating material has a void or discontinuity, a discharge can occur within the solid insulation. A void is shown in Figure 1. 6 It can be thought of as a tiny capacitor in a solid insulator filled with air, as shown in Figure 1. The air has a much lower dielectric constant than the surrounding mold compound, so its capacitance is small. In a series of capacitors, the lower the capacitance, the higher the voltage across the capacitor. The void has a higher electric field than the surrounding solid insulation.

Additionally, the voids are filled with air, a material with an extremely low dielectric breakdown, which causes the air in the void to break down, creating a plasma discharge that expands the void, eventually penetrating the remaining solid insulation and widening the void, providing a low resistance path through the insulation and causing a breakdown in the insulating material itself.

Figure 6: Partial discharge in a void *Provided by Allegro MicroSystems

Partial discharges can be detected with relatively simple electrical testing. Plasma discharges appear as current spikes in an applied voltage. Partial discharges occur in any type of insulation if the voltage is high enough. If partial discharge occurs near the working voltage it is an indication of a potentially short-lived device. Many standards now require partial discharge testing of reinforced insulation devices on the assembly line as part of insulation testing.

■ Overvoltage category
Overvoltage categories are used to determine the magnitude of lightning impulse transient voltages (V _IMPULSE) that equipment may encounter when connected to the power grid. The further the application is from the power grid, the lower the overvoltage category and the lower the transients that can be expected at that point (see Table 3).

For example, equipment that uses a 240V mains supply installed outside a building falls into Overvoltage Category IV and must be designed to withstand a lightning strike of 6000V _PK, while equipment that plugs into a socket inside a building falls into Overvoltage Category II and only needs to be designed to withstand 2500V _PK.

Inquiry

If you have any questions regarding this article, please contact us below.