Datasheet

Data Sheet ADuM3160
Rev. C | Page 11 of 16
The pulses at the transformer output have an amplitude greater
than 1.0 V. The decoder has a sensing threshold at approximately
0.5 V, thus establishing a 0.5 V margin in which induced voltages
can be tolerated. The voltage induced across the receiving coil is
given by
V = (−dβ/dt) ∑ πr
n
2
; n = 1, 2, … , N
where:
β is the magnetic flux density (gauss).
r
n
is the radius of the n
th
turn in the receiving coil (cm).
N is the number of turns in the receiving coil.
Given the geometry of the receiving coil in the ADuM3160 and
an imposed requirement that the induced voltage be, at most,
50% of the 0.5 V margin at the decoder, a maximum allowable
magnetic field is calculated as shown in Figure 6.
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE MAGNETIC FLUX
DENSITY (kgauss)
1k
0.001
100
100M
10
1
0.1
0.01
10k 100k 1M
10M
09125-006
Figure 6. Maximum Allowable External Magnetic Flux Density
For example, at a magnetic field frequency of 1 MHz, the maxi-
mum allowable magnetic field of 0.2 kgauss induces a voltage of
0.25 V at the receiving coil. This voltage is approximately 50% of
the sensing threshold and does not cause a faulty output transition.
Similarly, if such an event occurs during a transmitted pulse (and
is of the worst-case polarity), it reduces the received pulse from
>1.0 V to 0.75 V—still well above the 0.5 V sensing threshold of
the decoder.
The preceding magnetic flux density values correspond to specific
current magnitudes at given distances from the ADuM3160 trans-
formers. Figure 7 expresses these allowable current magnitudes
as a function of frequency for selected distances. As shown in
Figure 7, the ADuM3160 is extremely immune and can be affected
only by extremely large currents operated at high frequency very
close to the component. For the 1 MHz example noted, a 0.5 kA
current must be placed 5 mm away from the ADuM3160 to affect
the operation of the device.
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE CURRENT (kA)
1000
100
10
1
0.1
0.01
1k 10k
100M100k 1M 10M
DISTANCE = 5mm
DISTANCE = 1m
DISTANCE = 100mm
09125-007
Figure 7. Maximum Allowable Current
for Various Current-to-ADuM3160 Spacings
Note that at combinations of strong magnetic field and high
frequency, any loops formed by PCB traces may induce error
voltages sufficiently large to trigger the thresholds of succeeding
circuitry. Care should be taken in the layout of such traces to
avoid this possibility.
INSULATION LIFETIME
All insulation structures eventually break down when subjected
to voltage stress over a sufficiently long period. The rate of insu-
lation 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 ADuM3160.
Analog Devices performs accelerated life testing using voltage
levels higher than the rated continuous working voltage. Accel-
eration 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 50 years of service life for a bipolar ac operating
condition and the maximum CSA/VDE approved working volt-
ages. In many cases, the approved working voltage is higher than
the 50-year service life voltage. Operation at these high working
voltages can lead to shortened insulation life in some cases.
The insulation lifetime of the ADuM3160 depends on the
voltage waveform type imposed across the isolation barrier.
The iCoupler insulation structure degrades at different rates
depending on whether the waveform is bipolar ac, unipolar ac,
or dc. Figure 8, Figure 9, and Figure 10 illustrate these different
isolation voltage waveforms.
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