ADuM1280/ADuM1281/ADuM1285/ADuM1286 Data Sheet
Rev. D | Page 16 of 18
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 ADuM1280/ADuM1281/
ADuM1285/ADuM1286.
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 the 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 ADuM1280/ADuM1281/
ADuM1285/ADuM1286 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 15, Figure 16, and
Figure 17 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 16 or Figure 17 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
sinusoidal 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.
0V
RATED PEAK VOLTAGE
10444-015
Figure 15. Bipolar AC Waveform
0V
RATED PEAK VOLTAGE
10444-016
Figure 16. Unipolar AC Waveform
0V
RATED PEAK VOLTAGE
10444-017
Figure 17. DC Waveform