ADN4621 datasheet(23/24 Pages) AD

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Data Sheet

ADN4620/ADN4621

APPLICATIONS INFORMATION

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Rev. 0 | 23 of 24

Calculation and Use of Parameters Example

The following example frequently arises in power conversion appli-

cations. 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, clear-

ance, and lifetime of a device, see Figure 39 and the following

equations.

The working voltage across the barrier from Equation 1 is

VRMS = VACRMS2+VDC2

(2)

VRMS= 2402+4002

(3)

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.

VACRMS= VRMS2−VDC2

(4)

VACRMS = 4662−4002

(5)

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. Table 11 compares the value to the limits for the

working voltage for the expected lifetime. Note that the dc working

voltage limit in Table 11 is set by the creepage of the package as

specified in IEC 60664-1. This value can differ for specific system

level standards.

Figure 39. Critical Voltage Example

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