Data Sheet
ADuM240D/ADuM240E/ADuM241D/ADuM241E/ADuM242D/ADuM242E
system level standard and is based on the total rms voltage
across the isolation, pollution degree, and material group. The
material group and creepage for the ADuM240D/ADuM240E/
ADuM241D/ADuM241E/ADuM242D/ADuM242E isolators
are presented in Table 9.
Calculation and Use of Parameters Example
The following example frequently arises in power conversion
applications. Assume that the line voltage on one side of the
isolation is 240 V ac rms and a 400 V dc bus voltage is present
on the other side of the isolation barrier. The isolator material is
polyimide. To establish the critical voltages in determining the
creepage, clearance, and lifetime of a device, see Figure 24 and
the following equations.
Insulation Wear Out
The lifetime of insulation caused by wear out is determined by
its thickness, material properties, and the voltage stress applied.
It is important to verify that the product lifetime is adequate at
the application working voltage. The working voltage supported
by an isolator for wear out may not be the same as the working
voltage supported for tracking. The working voltage applicable
to tracking is specified in most standards.
V
AC RMS
Testing and modeling have shown that the primary driver of long-
term degradation is displacement current in the polyimide
insulation causing incremental damage. The stress on the insula-
tion can be broken down into broad categories, such as dc
stress, which causes very little wear out because there is no
displacement current, and an ac component time varying
voltage stress, which causes wear out.
V
V
V
DC
PEAK
RMS
TIME
Figure 24. Critical Voltage Example
The ratings in certification documents are usually based on
60 Hz sinusoidal stress because this reflects isolation from line
voltage. However, many practical applications have combinations
of 60 Hz ac and dc across the barrier as shown in Equation 1.
Because only the ac portion of the stress causes wear out, the
equation can be rearranged to solve for the ac rms voltage, as is
shown in Equation 2. For insulation wear out with the
polyimide materials used in these products, the ac rms voltage
determines the product lifetime.
The working voltage across the barrier from Equation 1 is
2
V
RMS VAC RMS2 VDC
2
2
V
RMS 240 400
V
RMS = 466 V
This VRMS value is the working voltage used together with the
material group and pollution degree when looking up the
creepage required by a system standard.
2
V
RMS VAC RMS2 VDC
(1)
To determine if the lifetime is adequate, obtain the time varying
portion of the working voltage. To obtain the ac rms voltage,
use Equation 2.
or
2
V
ACRMS V 2 VDC
(2)
RMS
2
V
ACRMS V 2 VDC
RMS
where:
2
V
AC RMS 466 4002
V
V
V
RMS is the total rms working voltage.
AC RMS is the time varying portion of the working voltage.
DC is the dc offset of the working voltage.
V
AC RMS = 240 V rms
In this case, the ac rms voltage is simply the line voltage of
240 V rms. This calculation is more relevant when the waveform is
not sinusoidal. The value is compared to the limits for working
voltage in Table 17 for the expected lifetime, less than a 60 Hz
sine wave, and it is well within the limit for a 50-year service life.
Note that the dc working voltage limit in Table 17 is set by the
creepage of the package as specified in IEC 60664-1. This value
can differ for specific system level standards.
Rev. D | Page 23 of 26
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