ADuM7701
Data Sheet
Minimize series resistance in the analog inputs to avoid any
INTERFACING TO ADSP-CM4xx
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.
The ADSP-CM4xx family of mixed-signal control processors
contains an on-chip sinc filter and clock generation modules for
direct connection to the ADuM7701 MCLKIN and MDAT pins.
The ADSP-CM4xx can process bit streams from four
ADuM7701 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
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 ADuM7701.
Figure 32 shows the typical interface between the ADuM7701
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.
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.
SINC PAIR n
PRIMARY
SINC0_D0
LIMIT
MDAT
SECONDARY
These tests subjected the ADuM7701 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:
CONTROL FOR GROUP n
SINC0_CLK0
MODULATOR CLOCK n
MCLKIN
ADuM77011
ADSP-CM40xF1
1
ADDITIONAL PINS OMITTED FOR CLARITY
Figure 32. Interfacing the ADuM7701 to the ADSP-CM4xx
The value that ensures at least a 37.5 year lifetime of
continuous (reinforced) use.
The maximum VDE approved working voltage.
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 used as close to the supply pins as
possible.
The lifetime of the ADuM7701 is guaranteed using a bipolar
ac waveform as shown in Figure 33.
RATED PEAK VOLTAGE
0V
Figure 33. Bipolar AC Waveform, 50 Hz or 60 Hz
Rev. 0 | Page 20 of 22
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