Datasheet

ADM2483
Rev. B | Page 16 of 20
Given the geometry of the receiving coil and an imposed
requirement that the induced voltage is, at most, 50% of the
0.5 V margin at the decoder, a maximum allowable magnetic
field is calculated, as shown in Figure 27.
100.000
10.000
1.000
0.100
0.010
0.001
1k 10k 100k 1M 10M 100M
04736-027
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE MAGNETIC
FLUX DENSITY (kGAUSS)
Figure 27. Maximum Allowable External Magnetic Flux Density
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 occurs during a transmitted pulse and
is the worst-case polarity, it reduces the received pulse from
>1.0 V to 0.75 V. This is well above the 0.5 V sensing threshold
of the decoder.
These magnetic flux density values are shown in Figure 28,
using more familiar quantities such as maximum allowable
current flow, at given distances away from the ADM2483
transformers.
1000.00
100.00
0.10
1.00
10.00
0.01
1k 10k 100k 1M 10M 100M
04736-028
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE CURRENT (kA)
DISTANCE = 1m
DISTANCE = 5mm
DISTANCE = 100mm
Figure 28. Maximum Allowable Current for Various
Current-to-ADM2483 Spacings
At combinations of strong magnetic field and high frequency,
any loops formed by printed circuit board traces could induce
large enough error voltages to trigger the thresholds of
succeeding circuitry. To avoid this possibility, care should be
taken in the layout of such traces.