ADuM1100 Data Sheet
Rev. K | Page 18 of 20
Given the geometry of the receiving coil in the ADuM1100 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 19.
MAGNETIC FIELD FREQUENCY (Hz)
100
MAXIMUM ALLOWABLE MAGNETIC FLUX
DENSITY (kgauss)
0.001
10
0.01
0.1
1
1k 10k 100k 1M 10M 100M
02462-019
Figure 19. Maximum Allowable External Magnetic Field
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 would reduce 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
ADuM1100 transformers. Figure 20 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As can be seen, the ADuM1100 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 ADuM1100 to affect the compone nt’s
operation.
MAGNETIC FIELD FREQUENCY (Hz)
1000
MAXIMUM ALLOWABLE CURRENT (kA)
0.01
100
0.1
1
10
1k
10k 100k
1M 10M 100M
02462-020
DISTANCE = 1m
DISTANCE = 100mm
DISTANCE = 5mm
Figure 20. Maximum Allowable Current for
Various Current-to-ADuM1100 Spacings
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 ADuM1100 isolator is a function of
the supply voltage, the input data rate, and the output load.
The input supply current is given by
I
DDI
= I
DDI (Q)
f ≤ 0.5f
r
I
DDI
= I
DDI (D)
× (2f − f
r
) + I
DDI (Q)
f > 0.5f
r
The output supply current is given by
I
DDO
= I
DDO (Q)
f ≤ 0.5f
r
I
DDO
= (I
DDO (D)
+ (0.5 × 10
−3
) × C
L
V
DDO
) × (2f − f
r
) + I
DDO (Q)
f > 0.5f
r
where:
I
DDI (D)
, I
DDO (D)
are the input and output dynamic supply currents
per channel (mA/Mbps).
C
L
is the output load capacitance (pF).
V
DDO
is the output supply voltage (V).
f is the input logic signal frequency (MHz, half the input data
rate, NRZ signaling).
f
r
is the input stage refresh rate (Mbps).
I
DDI (Q)
, I
DDO (Q)
are the specified input and output quiescent
supply currents (mA).
