adm2481 Analog Devices, Inc., adm2481 Datasheet - Page 15

• Manufacturer Part Number: adm2481
• Description: Half-duplex, Icoupler Isolated Rs-485 Transceiver Adm2481
• Manufacturer: Analog Devices, Inc.

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.
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.
100.000
10.000
Figure 27. Maximum Allowable External Magnetic Flux Density
1.000
0.100
0.010
0.001
1k
10k
MAGNETIC FIELD FREQUENCY (Hz)
100k
1M
10M
100M
Rev. 0 | Page 15 of 20
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 ADM2481
transformers.
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 succeed-
ing circuitry. To avoid this possibility, take care in the layout of
such traces.
1000.00
100.00
10.00
1.00
0.10
0.01
1k
Figure 28. Maximum Allowable Current for Various
DISTANCE = 5mm
DISTANCE = 100mm
10k
Current-to-ADM2481 Spacings
MAGNETIC FIELD FREQUENCY (Hz)
100k
DISTANCE = 1m
1M
10M
ADM2481
100M