adum3400 Analog Devices, Inc., adum3400 Datasheet - Page 21

• Manufacturer Part Number: adum3400
• Description: Quad-channel, Digital Isolators, Enhanced System-level Esd Reliability
• Manufacturer: Analog Devices, Inc.

The pulses at the transformer output have an amplitude greater
than 1.0 V. The decoder has a sensing threshold at about 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
where:
β is magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
Given the geometry of the receiving coil in the ADuM340x 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 19.
For example, at a magnetic field frequency of 1 MHz, the
maximum allowable magnetic field of 0.2 kgauss induces a
voltage of 0.25 V at the receiving coil. This is about 50% of the
sensing threshold and does not cause a faulty output transition.
Similarly, if such an event were to occur during a transmitted
pulse (and was of the worst-case polarity), it would reduce the
received pulse from >1.0 V to 0.75 V—still well above the 0.5 V
sensing threshold of the decoder.
n
is the radius of the n
V = (−dβ/dt)
0.001
Figure 19. Maximum Allowable External Magnetic Flux Density
0.01
100
0.1
10
1
1k
∑
10k
∏r
MAGNETIC FIELD FREQUENCY (Hz)
n
th
2
; n = 1, 2, … , N
turn in the receiving coil (cm).
100k
1M
10M
100M
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The preceding magnetic flux density values correspond to
specific current magnitudes at given distances from the
ADuM340x transformers. Figure 20 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As shown, the ADuM340x 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, one would have to place a 0.5 kA current 5 mm
away from the ADuM340x to affect the component’s operation.
Note that at combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board traces
could induce error voltages sufficiently large enough to trigger
the thresholds of succeeding circuitry. Care should be taken in
the layout of such traces to avoid this possibility.
1000
0.01
100
0.1
10
1
1k
ADuM3400/ADuM3401/ADuM3402
DISTANCE = 100mm
for Various Current-to-ADuM340x Spacings
Figure 20. Maximum Allowable Current
DISTANCE = 5mm
10k
MAGNETIC FIELD FREQUENCY (Hz)
100k
1M
DISTANCE = 1m
10M
100M