AD7400 Analog Devices, AD7400 Datasheet - Page 17

• Manufacturer Part Number: AD7400
• Description: Isolated Sigma-Delta Modulator
• Manufacturer: Analog Devices

Specifications of AD7400

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 10MSPS
• Interface: Ser
• Analog Input Type: Diff-Uni
• Ain Range: ± 0.2 V Diff,0.4 V p-p
• Adc Architecture: Sigma-Delta Modulator
• Pkg Type: SOIC

APPLICATIONS INFORMATION
GROUNDING AND LAYOUT
Supply decoupling with a value of 100 nF is strongly recom-
mended on both V
V
applications 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
may cause voltage differentials between pins to exceed the
absolute maximum ratings of the device, 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 AD7400 PERFORMANCE
A simple standalone AD7400 evaluation board is available with
split ground planes and a board split beneath the AD7400
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 AD7400.
DD1
pins does not significantly affect performance. In
DD1
and V
DD2
. Decoupling on one or both
Rev. E | Page 17 of 20
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:
•
•
It should also be noted that the lifetime of the AD7400 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 29, Figure 30, and Figure 31 illustrate the different
isolation voltage waveforms.
The value that ensures at least a 50-year lifetime of
continuous use
The maximum CSA/VDE approved working voltage
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
0V
0V
0V
Figure 30. Unipolar AC Waveform
Figure 29. Bipolar AC Waveform
Figure 31. DC Waveform
AD7400