AD7402 datasheet(19/20 Pages) AD

19 / 20 page

Data Sheet

AD7402

Rev. A | Page 19 of 20

POWER SUPPLY CONSIDERATIONS

The AD7402 requires a 5 V VDD1 supply, and there are various

means of achieving this. One method is to use an isolated dc-to-

dc converter such as the ADuM6000. This method provides a 5 V

regulated dc supply across the isolation barrier. Note that the

inherent isolation of the ADuM6000 is lower than the AD7402.

Figure 35. ADuM6000 Isolated 5 V DC-to-DC Regulator Example

Another method is to regulate a dc supply on the high voltage

side of the isolation barrier using a step-down dc-to-dc regulator,

such as the ADP2441.

Figure 36. ADP2441 Step-Down DC-to-DC Regulator Example

GROUNDING AND LAYOUT

It is recommended to decouple the VDD1 supply with a 10 μF

capacitor in parallel with a 1 nF capacitor to GND1. Decouple

the VDD2 supply with a 100 nF value to GND2. In applications

involving high common-mode transients, ensure that board

coupling across the isolation barrier is minimized.

Furthermore, design the board layout so that any coupling that

occurs equally affects all pins on a given component side.

Failure to ensure equal coupling can cause voltage differentials

between pins to exceed the absolute maximum ratings of the

device, thereby leading to latch-up or permanent damage. Place

any decoupling used as close to the supply pins as possible.

Minimize series resistance in the analog inputs to avoid any

distortion effects, especially at high temperatures. If possible,

equalize the source impedance on each analog input to minimize

offset. Check for mismatch and thermocouple effects on the analog

input printed circuit board (PCB) tracks to reduce offset drift.

INSULATION LIFETIME

All insulation structures eventually break down when subjected

to voltage stress over a sufficiently long period. The rate of

insulation degradation is dependent on the characteristics of the

voltage waveform applied across the insulation. In addition to

the testing performed by the regulatory agencies, Analog

Devices carries out an extensive set of evaluations to determine

the lifetime of the insulation structure within the AD7402.

Analog Devices performs accelerated life testing using voltage

levels higher than the rated continuous working voltage.

Acceleration factors for several operating conditions are

determined. These factors allow calculation of the time to

failure at the actual working voltage. The values shown in Table 8

summarize the peak voltage for 20 years of service life for a

bipolar, ac operating condition and the maximum VDE

approved working voltages.

These tests subjected the AD7402 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 the acceleration factors. These factors were then used

to calculate the time to failure under the normal operating

conditions. The values shown in Table 8 are the lesser of the

following two values:



The value that ensures at least a 20-year lifetime of

continuous use.



The maximum VDE approved working voltage.

Note that the lifetime of the AD7402 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 37, Figure 38, and Figure 39 illustrate the different

isolation voltage waveforms.

Figure 37. Bipolar AC Waveform, 50 Hz or 60 Hz

Figure 38. Unipolar AC Waveform, 50 Hz or 60 Hz

Figure 39. DC Waveform

5V DIGITAL

ISOLATION

BARRIER

VDD1

VDD2

5V ISO

VDD2

VDD1

5V DIGITAL

4.5V TO 36V

ADP2441

DC-TO-DC

SWITCHING

REGULATOR

ISOLATION

BARRIER

RATED PEAK VOLTAGE

AD7402 Datasheet(PDF) 19 Page - Analog Devices

AD7402 Datasheet(HTML) 19 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL