Datasheet

Data Sheet ADuM2400/ADuM2401/ADuM2402
Rev. E | Page 19 of 24
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
ADuM240x transformers. Figure 20 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As can be seen, the ADuM240x is 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, place a 0.5 kA current 5 mm away from the
ADuM240x to affect the component’s operation.
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE CURRENT (kA)
1000
100
10
1
0.1
0.01
1k 10k 100M100k 1M 10M
DISTANCE = 5mm
DISTANCE = 1m
DISTANCE = 100mm
05007-020
Figure 20. Maximum Allowable Current for
Various Current-to-ADuM240x 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 at a given channel of the ADuM240x isolator is
a function of the supply voltage, the data rate of the channel,
and the output load of the channel.
For each input channel, the 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
For each output channel, the 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 of 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).
To calculate the total I
DD1
and I
DD2
, the supply currents for each
input and output channel corresponding to I
DD1
and I
DD2
are
calculated and totaled. Figure 8 and Figure 9 provide per channel
supply currents as a function of data rate for an unloaded output
condition. Figure 10 provides per channel supply current as a
function of data rate for a 15 pF output condition. Figure 11
through Figure 15 provide the total I
DD1
and I
DD2
as a function of
data rate for the ADuM2400/ADuM2401/ADuM2402 channel
configurations.