AD7401

Rev. A | Page 17 of 20

APPLICATION INFORMATION

GROUNDING AND LAYOUT

Supply decoupling with a value of 100 nF is strongly recom-

involving high common-mode transients, care should be taken

to ensure that board coupling across the isolation barrier is

minimized. Furthermore, the board layout should be designed

so that any coupling that occurs equally affects all pins on a

given component side. Failure to ensure this could cause voltage

differentials between pins to exceed the device’s absolute

maximum ratings, thereby leading to latch-up or permanent

damage. Any decoupling used should be placed as close to the

supply pins as possible.

Series resistance in the analog inputs should be minimized to

avoid any distortion effects, especially at high temperatures. If

possible, equalize the source impedance on each analog input to

minimize offset. Beware of mismatch and thermocouple effects

on the analog input PCB tracks to reduce offset drift.

EVALUATING THE AD7401 PERFORMANCE

A simple standalone AD7401 evaluation board is available with

split ground planes and a board split beneath the AD7401

package to ensure isolation. This board allows access to each

pin on the device for evaluation purposes. External supplies and

all other circuitry (such as a digital filter) must be provided by

the user.

INSULATION LIFETIME

All insulation structures, subjected to sufficient time and/or

voltage, are vulnerable to breakdown. In addition to the testing

performed by the regulatory agencies, Analog Devices has

carried out an extensive set of evaluations to determine the

lifetime of the insulation structure within the AD7401.

These tests subjected populations of devices to continuous

cross-isolation voltages. To accelerate the occurrence of failures,

the selected test voltages were values exceeding those of normal

use. The time to failure values of these units were recorded and

used to calculate acceleration factors. These factors were then

used to calculate the time to failure under normal operating

conditions. The values shown in Table 7 are the lesser of the

following two values:

•

The value that ensures at least a 50-year lifetime of

continuous use.

•

The maximum CSA/VDE approved working voltage.

It should also be noted that the lifetime of the AD7401 varies

according to the waveform type imposed across the isolation

barrier. The iCoupler insulation structure is stressed differently

depending on whether the waveform is bipolar ac, unipolar ac,

or dc. Figure 30, Figure 31, and Figure 32 illustrate the different

isolation voltage waveforms.

0V

RATED PEAK VOLTAGE

Figure 30. Bipolar AC Waveform

0V

RATED PEAK VOLTAGE

Figure 31. Unipolar AC Waveform

0V

RATED PEAK VOLTAGE

Figure 32. DC Waveform