ADuM2280CRIZ datasheet(16/20 Pages) AD

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ADuM2280/ADuM2281/ADuM2285/ADuM2286

Data Sheet

Rev. 0 | Page 16 of 20

INSULATION LIFETIME

All insulation structures eventually break down when subjected

to voltage stress over a sufficiently long period. The rate of

insulation degradation is dependent on the characteristics of

the voltage waveform applied across the insulation. In addition

to the testing performed by the regulatory agencies, Analog

Devices carries out an extensive set of evaluations to determine

the lifetime of the insulation structure within the ADuM228x.

Analog Devices performs accelerated life testing using voltage

levels higher than the rated continuous working voltage.

Acceleration factors for several operating conditions are

determined. These factors allow calculation of the time to

failure at the actual working voltage. The values shown in

Table 19 summarize the peak voltage for 50 years of service

life for a bipolar ac operating condition and the maximum

CSA/VDE approved working voltages. In many cases, the

approved working voltage is higher than 50-year service life

voltage. Operation at these high working voltages can lead to

shortened insulation life in some cases.

The insulation lifetime of the ADuM228x depends on the

voltage waveform type imposed across the isolation barrier.

The iCoupler insulation structure degrades at different rates

depending on whether the waveform is bipolar ac, unipolar

ac, or dc. Figure 16, Figure 17, and Figure 18 illustrate these

different isolation voltage waveforms.

Bipolar ac voltage is the most stringent environment. The goal

of a 50-year operating lifetime under the ac bipolar condition

determines the Analog Devices recommended maximum

working voltage.

In the case of unipolar ac or dc voltage, the stress on the

insulation is significantly lower. This allows operation at higher

working voltages while still achieving a 50-year service life.

The working voltages listed in Table 19 can be applied while

maintaining the 50-year minimum lifetime provided the voltage

conforms to either the unipolar ac or dc voltage case. Any cross-

insulation voltage waveform that does not conform to Figure 17

or Figure 18 should be treated as a bipolar ac waveform, and its

peak voltage should be limited to the 50-year lifetime voltage

value listed in Table 19.

Note that the voltage presented in Figure 17 is shown as sinu-

soidal for illustration purposes only. It is meant to represent any

voltage waveform varying between 0 V and some limiting value.

The limiting value can be positive or negative, but the voltage

cannot cross 0 V.

RATED PEAK VOLTAGE

Figure 16. Bipolar AC Waveform

RATED PEAK VOLTAGE

Figure 17. Unipolar AC Waveform

RATED PEAK VOLTAGE

Figure 18. DC Waveform

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