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ADuM1310/ADuM1311
Rev. F | Page 19 of 20
0
MAGNETIC FIELD FREQUENCY (Hz)
M
D
1k
0.001
100
100M
10
1
0.1
0.01
10k
100k
1M
10M
Figure 15. Maximum Allowable External Magnetic Flux Density
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 from the
ADuM131x transformers. Figure 16 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As shown, the ADuM131x is 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 noted, one would have to place a 0.5 kA current 5 mm
away from the ADuM131x to affect the component’s operation.
MAGNETIC FIELD FREQUENCY (Hz)
Figure 16. Maximum Allowable Current
M
1000
100
10
1
0.1
0.01
1k
10k
100M
100k
1M
10M
DISTANCE = 5mm
DISTANCE = 1m
DISTANCE = 100mm
0
for Various Current-to-ADuM131x Spacings
Note that at combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board traces can
induce error voltages sufficient to trigger succeeding circuitry.
Care should be taken in the layout of such traces to avoid this
possibility.
POWER CONSUMPTION
The supply current at a given channel of the ADuM131x
isolator is a function of the supply voltage, the channel’s data
rate, and the channel’s output load.
For each input channel, the supply current is given by
I
DDI
= I
DDI
(
Q
)
I
DDI
=
I
DDI (D)
× (2
f
f
r
) +
I
DDI
(
Q
)
For each output channel, the supply current is given by
I
DDO
= I
DDO
(
Q
)
I
DDO
= (
I
DDO
(
D
)
+ (0.5 × 10
3
) ×
C
L
× V
DDO
) × (2
f f
r
) +
I
DDO
(
Q
)
f
≤ 0.5
f
r
f
> 0.5
f
r
f
≤ 0.5
f
r
f
> 0.5
f
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); it is half of the input
data rate expressed in units of Mbps.
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).
To calculate the total V
DD1
and V
DD2
supply current, the supply
currents for each input and output channel corresponding to
V
DD1
and V
DD2
are calculated and totaled. The ADuM131x
contains an internal data channel that is not available to the
user. This channel is in the same orientation as Channel A and
consumes quiescent current. The contribution of this channel
must be included in the total quiescent current calculation for
each supply. Figure 6 and Figure 7 provide per-channel supply
currents as a function of data rate for an unloaded output
condition. Figure 8 provides per-channel supply current as a
function of data rate for a 15 pF output condition. Figure 9
through Figure 12 provide total V
DD1
and V
DD2
supply current as
a function of data rate for ADuM1310/ADuM1311 channel
configurations.