adum3100 Analog Devices, Inc., adum3100 Datasheet - Page 15

• Manufacturer Part Number: adum3100
• Description: Digital Isolator, Enhanced System-level Esd Reliability
• Manufacturer: Analog Devices, Inc.

Given the geometry of the receiving coil in the ADuM3100 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 18.
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 reduces the
received pulse from >1.0 V to 0.75 V—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 away from
the ADuM3100 transformers. Figure 19 shows the allowable
current magnitudes as a function of frequency for selected
distances. As can be seen, the ADuM3100 is extremely immune
and can be affected only by extremely large currents operated at
high frequency and very close to the component. For the 1 MHz
example noted, one would have to place a current of 0.5 kA
5 mm away from the ADuM3100 to affect the component’s
operation.
0.001
0.01
100
0.1
10
Figure 18. Maximum Allowable External Magnetic Field
1
1k
10k
MAGNETIC FIELD FREQUENCY (Hz)
100k
1M
10M
100M
Rev. A | Page 15 of 16
Note that at combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board traces
could induce sufficiently large error voltages to trigger the
thresholds of succeeding circuitry. Care should be taken in
the layout of such traces to avoid this possibility.
POWER CONSUMPTION
The supply current of the ADuM3100 isolator is a function of
the supply voltage, the input data rate, and the output load.
The input supply current is given by
The output supply current is given by
where:
I
per channel (mA/Mbps).
C
V
f is the input logic signal frequency (MHz, half of the input data
rate, NRZ signaling).
f
I
supply currents (mA).
Figure 19. Maximum Allowable Current for Current-to-ADuM3100 Spacings
r
DDI (D)
DDI (Q)
L
DDO
is the input stage refresh rate (Mbps).
is output load capacitance (pF).
I
I
I
I
is the output supply voltage (V).
DDI
DDI
DDO
DDO
, I
, I
1000
0.01
DDO (D)
DDO (Q)
100
0.1
10
= I
= I
= I
= (I
1
1k
DDI (D)
DDI (Q)
DDO (Q)
DISTANCE = 100mm
DDO (D)
are the input and output dynamic supply currents
are the specified input and output quiescent
× (2f – f
+ (0.5 × 10
10k
MAGNETIC FIELD FREQUENCY (Hz)
DISTANCE = 5mm
r
) + I
100k
DDI (Q)
−3
) × C
L
V
1M
DDO
DISTANCE = 1m
) × (2f – f
ADuM3100
10M
r
) + I
f ≤ 0.5f
f > 0.5f
f ≤ 0.5f
f > 0.5f
DDO (Q)
100M
r
r
r
r