Insulation lifetime projection data is collected by using industry-standard Time Dependent Dielectric Breakdown (TDDB) test method. In this test, all pins on each side of the barrier are tied together creating a two-terminal device and high voltage applied between the two sides; See Figure 9-7 for TDDB test setup. The insulation breakdown data is collected at various high voltages switching at 60 Hz over temperature. For basic insulation, VDE standard requires the use of TDDB projection line with failure rate of less than 1000 part per million (ppm). For reinforced insulation, VDE standard requires the use of TDDB projection line with failure rate of less than 1 part per million (ppm).

Even though the expected minimum insulation lifetime is 20 years, at the specified working isolation voltage, VDE basic and reinforced certifications require additional safety margin of 20% for working voltage. For basic certification, device lifetime requires a safety margin of 20% translating to a minimum required insulation lifetime of 24 years at a working voltage that is 20% higher than the specified value.

Figure 9-8 shows the intrinsic capability of the isolation barrier to withstand high voltage stress over its lifetime. Based on the TDDB data, the intrinsic capability of the insulation is 450 V_RMS with a lifetime of >100 years in the 8D package . Other factors, such as package size, pollution degree, material group, etc. can further limit the working voltage of the component. At the lower working voltages, the corresponding insulation lifetime is much longer than 100 years in the 8-D package.

Figure 9-7 Test Setup for Insulation Lifetime Measurement

Figure 9-8 Insulation Lifetime Projection Data for 8-D Package