adum3440 Analog Devices, Inc., adum3440 Datasheet - Page 20

• Manufacturer Part Number: adum3440
• Description: Quad Channel, High Speed Digital Isolators
• Manufacturer: Analog Devices, Inc.

ADuM3440/ADuM3441/ADuM3442
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 ADuM344x.
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
Figure 20 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 ADuM344x 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 20, Figure 21, and Figure 22 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 maximum working voltage recommended by
Analog Devices.
In the case of unipolar ac or dc voltage, the stress on the
insulation is significantly lower, which allows operation at
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higher working voltages while still achieving a 50-year service
life. The working voltages listed in Table 10 can be applied while
maintaining the 50-year minimum lifetime provided the voltage
conforms to either the unipolar ac or dc voltage cases. Any cross
insulation voltage waveform that does not conform to Figure 21
or Figure 22 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 10.
Note that the voltage presented in Figure 21 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.
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
0V
0V
0V
Figure 21. Unipolar AC Waveform
Figure 20. Bipolar AC Waveform
Figure 22. DC Waveform