The significance of DIN VDE V 0884-11:2017-01 to the certification of digital isolators

“As of January 2020, the German Institute for Standardization (DIN) and the German Institute of Electrical Engineers (VDE) V0884-10: 2006-12 are no longer valid certification standards for evaluating the inherent insulation characteristics and high-voltage performance of electromagnetic and capacitive electrical isolation products . This marks the end of the three-year transition period for integrated circuit (IC) manufacturers. The transition period began in 2017, when VDE issued the updated DIN VDE V 0884-11:2017-01 standard. With this change, IC manufacturers must upgrade to meet the new certification requirements, otherwise they will be required to delete the VDE certification from the corresponding IC data sheet.

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Author: Luke Trowbridge

As of January 2020, the German Institute for Standardization (DIN) and the German Institute of Electrical Engineers (VDE) V0884-10: 2006-12 are no longer valid certification standards for evaluating the inherent insulation characteristics and high-voltage performance of electromagnetic and capacitive electrical isolation products . This marks the end of the three-year transition period for integrated circuit (IC) manufacturers. The transition period began in 2017, when VDE issued the updated DIN VDE V 0884-11:2017-01 standard. With this change, IC manufacturers must upgrade to meet the new certification requirements, otherwise they will be required to delete the VDE certification from the corresponding IC data sheet.

Because these certifications are the only device-level standards created for basic and enhanced digital isolators, they can convince original equipment manufacturers and terminal equipment manufacturers that using the isolator will meet their system-level high-voltage requirements and terminal equipment level certifications .

What are the changes in the new standard?

The biggest change from DIN V VDE V 0884-10 to DIN VDE V 0884-11 is the change to the certification process and requirements. The changes listed in Table 1 will affect the device standards for basic certification and enhanced certification.

Table 1: DIN V VDE update (basic and enhanced)

Let’s go through each update one by one.

The “Maximum Surge Isolation Voltage” quantifies the ability of an isolator to withstand extremely high voltage pulses of a specific transient curve. Due to direct or indirect lightning strikes, faults or short-circuit events, the surge test curve shown in Figure 2 may appear during the installation. Although the test voltage, minimum voltage requirements, and number of shocks have not changed, shocks are now performed with bipolar pulses instead of unipolar pulses. 25 positive pulses are applied, followed by a delay of 1 hour to 2 hours, and then 25 negative pulses are applied to the same device.

During a single surge pulse, some charge remains in the isolation dielectric, creating a residual electric field. In a unipolar test, the residual electric field reduces the total electric field experienced by the isolation barrier during subsequent pulses. Compared to a unipolar pulse, a bipolar pulse has a greater field strength to the isolation barrier because the remaining electric field is now superimposed on the previous pulse, which exceeds the field strength of any previous pulse in the device test sequence.

Figure 1: Surge test to simulate direct or indirect lightning strikes, faults or short-circuit events

Currently, DIN VDE V 0884-11 requires the use of the industry standard time-dependent dielectric breakdown (TDDB) test method to collect the life prediction data of the isolator. In this test, all the pins on each side of the isolation barrier are tied together to form a two-terminal device, and a high voltage is applied between the two sides. At room temperature and maximum operating temperature, various high-voltage switching at 60 Hz is used to collect insulation breakdown data.

Figure 2 shows the inherent ability of the isolation barrier to withstand high-pressure stress during its entire life. According to TDDB data, the inherent capacity of insulation is 1.5 kV_RMS, The service life is 135 years. Other factors such as package size, pollution degree, material type, etc. may further limit the operating voltage of the component. It takes months or even years for integrated circuit manufacturers to collect data for each certified device.

Figure 2: TDDB test data shows the inherent ability of the isolation barrier to withstand high pressure stress during its service life

For reinforced isolation, DIN VDE V 0884-11 requires the use of a TDDB prediction line with a failure rate of less than one part per million (ppm). Even if the expected minimum insulation life under the specified working isolation voltage is twenty years, the new enhanced certification still requires an additional 20% safety margin for the working voltage and a 87.5% safety margin for the rated life of the device, which is That is, when the working voltage is 20% higher than the specified value, the minimum required insulation life is 37.5 years.

For basic isolation, the requirements of DIN VDE V 0884-11 are not too strict, and the allowable failure rate is less than 1000 ppm. A working voltage margin of 20% is still required, but the service life margin of the basic insulation device is reduced to 30%, which means that when the working voltage is 20% higher than the rated value, the total required service life is 26 years. DIN V VDE V 0884-10 did not previously define the minimum rated life and the failure rate during the entire life.

Although the partial discharge test standard has not been changed in DIN VDE V 0884-11, it is very useful to understand the relevance of partial discharge tests to isolated components. Even if there is no partial discharge phenomenon in silicon dioxide, TI and VDE still test the partial discharge of digital isolators based on silicon dioxide. Optocouplers use partial discharge testing as a means to screen out poor mass-produced devices that form excess air bubbles in the dielectric. Although the partial discharge test can exclude defective devices, it should be noted that it cannot be used as a minimum guaranteed life test. Only the TDDB test performed on a digital isolator is an accurate life test process.

Through certification, equipment manufacturers can use isolation devices worldwide to meet the design requirements of their terminal applications and understand whether the isolator can work reliably throughout its life cycle. Updates and revisions to certification requirements (such as those in DIN VDE) ensure that high-voltage safety requirements are always meaningful and as strict as possible. If the device manufacturer cannot guarantee that it meets the requirements of DIN VDE V 0884-11, it becomes critical for the device manufacturer to inspect existing and future-designed circuit board isolation devices to ensure that they still meet the certification requirements.