Data Sheet

ADM3058E

Rev. A | Page 17 of 18

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 23

and the following equations.

TIME

Figure 23. Critical Voltage Example

The working voltage across the barrier from Equation 1 is

22

RMS

AC RMS

DC

VV

V



2

2

400

240 



RMS

V

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,

2

2

DC

RMS

RMS

AC

V

V

V





2

2

400

466 



RMS

AC

V

calculation is more relevant when the waveform is not sinusoidal.

The value is compared to the limits for working voltage in Table 10

for the expected lifetime, which is less than a 60 Hz sine wave,

and is well within the limit for a 50-year service life.

Note that the dc working voltage limit is set by the creepage of

the package as specified in IEC 60664-1. This value can differ

for specific system level standards.