EVAL-ADM2587EEBZ Analog Devices Inc, EVAL-ADM2587EEBZ Datasheet - Page 15

• Manufacturer Part Number: EVAL-ADM2587EEBZ
• Description: RS-485 Transceiver Eval. Board
• Manufacturer: Analog Devices Inc
• Series: isoPower®r

Specifications of EVAL-ADM2587EEBZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: Full/Half Duplex RS-485 Transceiver
• Kit Application Type: Interface
• Silicon Core Number: ADM2587
• Kit Contents: Board And Literature
• Main Purpose: Interface, Transceiver, RS-485
• Utilized Ic / Part: ADM2587
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DC CORRECTNESS AND MAGNETIC FIELD IMMUNITY
The digital signals transmit across the isolation barrier using
iCoupler technology. This technique uses chip-scale transformer
windings to couple the digital signals magnetically from one
side of the barrier to the other. Digital inputs are encoded into
waveforms that are capable of exciting the primary transformer
winding. At the secondary winding, the induced waveforms are
decoded into the binary value that was originally transmitted.
Positive and negative logic transitions at the isolator input cause
narrow (~1 ns) pulses to be sent to the decoder via the transformer.
The decoder is bistable and is, therefore, either set or reset by
the pulses, indicating input logic transitions. In the absence of
logic transitions at the input for more than 1 µs, periodic sets of
refresh pulses indicative of the correct input state are sent to
ensure dc correctness at the output. If the decoder receives no
internal pulses of more than approximately 5 μs, the input side
is assumed to be unpowered or nonfunctional, in which case,
the isolator output is forced to a default state by the watchdog
timer circuit.
This situation should occur in the ADM2582E/ADM2587E devices
only during power-up and power-down operations. The limitation
on the ADM2582E/ADM2587E magnetic field immunity is set
by the condition in which induced voltage in the transformer
receiving coil is sufficiently large to either falsely set or reset the
decoder. The following analysis defines the conditions under
which this can occur.
The 3.3 V operating condition of the ADM2582E/ADM2587E
is examined because it represents the most susceptible mode of
operation. The pulses at the transformer output have an amplitude
of >1.0 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 magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
Given the geometry of the receiving coil in the ADM2582E/
ADM2587E 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 33.
n
is the radius of the nth turn in the receiving coil (cm).
V = (−dβ/dt)Σπr
n
2; n = 1, 2, … , N
Rev. B | Page 15 of 20
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 of the worst-case polarity), it reduces the received pulse
from >1.0 V to 0.75 V, which is still well above the 0.5 V sensing
threshold of the decoder.
The preceding magnetic flux density values correspond
to specific current magnitudes at given distances from the
ADM2582E/ADM2587E transformers. Figure 34 expresses
these allowable current magnitudes as a function of frequency
for selected distances. As shown in Figure 34, the ADM2582E/
ADM2587E are 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, a 0.5 kA current must
be placed 5 mm away from the ADM2582E/ADM2587E to affect
component operation.
Note that in combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board (PCB)
traces can induce error voltages sufficiently large to trigger the
thresholds of succeeding circuitry. Take care in the layout of
such traces to avoid this possibility.
0.001
Figure 33. Maximum Allowable External Magnetic Flux Density
0.01
Figure 34. Maximum Allowable Current for Various Current-to-
0.01
100
100
0.1
0.1
1k
10
10
1
1
1k
1k
DISTANCE = 100mm
10k
10k
ADM2582E/ADM2587E Spacings
DISTANCE = 5mm
MAGNETIC FIELD FREQUENCY (Hz)
MAGNETIC FIELD FREQUENCY (Hz)
100k
100k
ADM2582E/ADM2587E
1M
1M
DISTANCE = 1m
10M
10M
100M
100M