ADuM7703
Data Sheet
INTERFACING TO ADSP-CM4xx
INSULATION LIFETIME
The ADSP-CM4xx family of mixed-signal control processors
contains an on-chip sinc filter and clock generation modules for
direct connection to the ADuM7703 MCLKIN and MDAT pins.
The ADSP-CM4xx can process bit streams from four ADuM7703
devices using a pair of configurable sinc filters for each bit stream.
The primary sinc filter of each pair produces the filtered and
decimated output for the pair. The output can be decimated to
any integer rate between 8 times and 256 times lower than the
input rate. The four secondary sinc filters are low latency filters
with programmable positive and negative overrange detection
comparators that can detect system fault conditions.
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 ADuM7703.
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 10 summarize the peak voltage
for 37.5 years of (reinforced) service life for a bipolar, ac operating
condition and the maximum VDE approved working voltages.
Figure 32 shows the typical interface between the ADuM7703
and the ADSP-CM4xx. Additional information on the
configuration of the sinc filter modules in the ADSP-CM4xx
can be found in the AN-1265 Application Note.
These tests subjected the ADuM7703 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 10 are the lesser of the
following two values:
SINC PAIR n
PRIMARY
SINC0_D0
LIMIT
MDAT
SECONDARY
CONTROL FOR GROUP n
SINC0_CLK0
The value that ensures at least a 37.5 year lifetime of
continuous (reinforced) use.
MODULATOR CLOCK n
MCLKIN
ADuM77031
ADSP-CM40xF1
The maximum VDE approved working voltage.
1
ADDITIONAL PINS OMITTED FOR CLARITY
The lifetime of the ADuM7703 is guaranteed using a bipolar
ac waveform, as shown in Figure 33.
Figure 32. Interfacing the ADuM7703 to the ADSP-CM4xx
GROUNDING AND LAYOUT
It is recommended to decouple the VDD1 supply with a 10 μF
capacitor in parallel with a 100 nF capacitor to GND1. Decouple
the VDD2 supply with a 10 μF capacitor in parallel with a 100 nF
capacitor 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 as close to the supply pins as possible.
RATED PEAK VOLTAGE
0V
Figure 33. Bipolar AC Waveform, 50 Hz or 60 Hz
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 PCB tracks to reduce offset drift.
Rev. 0 | Page 20 of 22
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