ADM3050EBRIZ datasheet(18/19 Pages) AD

18 / 19 page

ADM3050E

Data Sheet

Rev. B | Page 18 of 19

The ratings in certification documents are usually based on

60 Hz sinusoidal stress because this reflects isolation from line

voltage. 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 shown in

Equation 2. For insulation wear out with the polyimide materials

used in these products, the ac rms voltage determines the

product lifetime.

RMS

AC RMS

(1)

RMS

−

(2)

where:

VRMS is the total rms working voltage.

VAC RMS is the time varying portion of the working voltage.

VDC is the dc offset of the working voltage.

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 VDC 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 27 and

the following equations.

TIME

VAC RMS

VRMS

VDC

VPEAK

Figure 27. Critical Voltage Example

The working voltage across the barrier from Equation 1 is

RMS

AC RMS

400

240 +

RMS

VRMS = 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.

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.

RMS

−

400

466 −

RMS

VAC 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 11 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.

ADM3050EBRIZ Datasheet(PDF) 18 Page - Analog Devices

ADM3050EBRIZ Datasheet(HTML) 18 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL