ADM3054 AD [Analog Devices], ADM3054 Datasheet - Page 17

• Manufacturer Part Number: ADM3054
• Description: 5 kV rms Signal Isolated High Speed CAN Transceiver with Bus Protection
• Manufacturer: AD [Analog Devices]

Data Sheet
MAGNETIC FIELD IMMUNITY
The limitation on the magnetic field immunity of the iCoupler
is set by the condition in which an induced voltage in the receiving
coil of the transformer is large enough to either falsely set or
reset the decoder. The following analysis defines the conditions
under which this may occur. The 3 V operating condition of the
ADM3054
mode of operation.
The pulses at the transformer output have an amplitude greater
than 1 V. The decoder has a sensing threshold of 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 the magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
n
is the radius of the n
V
0.001
Figure 30. Maximum Allowable External Magnetic Flux Density
0.01
100
0.1
=
10
1
1k



is examined because it represents the most susceptible
−
dt
d
β



∑
10k
π
MAGNETIC FIELD FREQUENCY (Hz)
r
n
2
th
; n = 1, 2, …, N
turn in the receiving coil (cm).
100k
1M
10M
100M
Rev. 0 | Page 17 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 can be determined using Figure 30.
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 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 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.
Figure 31 shows the magnetic flux density values in terms of
more familiar quantities, such as maximum allowable current
flow at given distances away from the
With combinations of strong magnetic field and high frequency,
any loops formed by printed circuit board (PCB) traces can
induce error voltages large enough to trigger the thresholds of
succeeding circuitry. Therefore, care is necessary in the layout of
such traces to avoid this possibility.
1000
0.01
100
0.1
10
1
1k
DISTANCE = 5mm
Figure 31. Maximum Allowable Current for
Various
DISTANCE = 100mm
10k
MAGNETIC FIELD FREQUENCY (Hz)
Current-to-ADM3054
100k
ADM3054
DISTANCE = 1m
1M
Spacings
10M
transformers.
ADM3054
100M