adum3300 Analog Devices, Inc., adum3300 Datasheet - Page 18

• Manufacturer Part Number: adum3300
• Description: Triple-channel, Digital Isolators, Enhanced System-level Esd Reliability
• Manufacturer: Analog Devices, Inc.

ADuM3300/ADuM3301
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 ADuM330x 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 16.
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 16. Maximum Allowable External Magnetic Flux Density
0.01
100
0.1
10
1
1k
∑
10k
∏r
MAGNETIC FIELD FREQUENCY (Hz)
n
2
th
; n = 1, 2, … , N
turn in the receiving coil (cm).
100k
1M
10M
100M
Rev. 0 | Page 18 of 20
The preceding magnetic flux density values correspond to
specific current magnitudes at given distances from the
ADuM330x transformers. Figure 17 expresses these allowable
current magnitudes as a function of frequency for selected
distances. The ADuM330x is extremely immune and can be
affected only by extremely large currents operated at high
frequency very close to the component (see Figure 17). For the
1 MHz example noted, one would have to place a 0.5 kA current
5 mm away from the ADuM330x 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.
Figure 17. Maximum Allowable Current for Various Current-to-ADuM330x
1000
0.01
100
0.1
10
1
1k
DISTANCE = 100mm
DISTANCE = 5mm
10k
MAGNETIC FIELD FREQUENCY (Hz)
100k
Spacings
1M
DISTANCE = 1m
10M
100M