Data Sheet ADuM110N
Rev. 0 | Page 15 of 16
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 13 and
the following equations.
ISOL
TION VOLTAGE
TIME
V
AC RMS
V
RMS
V
DC
V
PEAK
13736-011
Figure 13. Critical Voltage Example
The working voltage across the barrier from Equation 1 is
V
RMS
=
22
DCRMSAC
VV
V
RMS
=
22
400240
V
RMS
= 466 V
This is the working voltage used together with the material
group and pollution degree when looking up the creepage
required by a system standard.
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.
22
DCRMSACRMS
VVV
22
400466
ACRMS
V
V
ACRMS
= 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 15 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 15 is set by the
creepage of the package as specified in IEC 60664-1. This value
can differ for specific system level standards.
