Datasheet

Data Sheet ADuM1200/ADuM1201
Rev. J | Page 25 of 28
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 has 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
ADuM1200/ADuM1201 transformers. Figure 14 expresses
these allowable current magnitudes as a function of frequency
for selected distances. As seen, the ADuM1200/ADuM1201 are
extremely immune and can be affected only by extremely large
currents operating very close to the component at a high
frequency. For the 1 MHz example, a 0.5 kA current would have
to be placed 5 mm away from the ADuM1200/ADuM1201 to
affect the operation of the component.
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
04642-014
Figure 14. Maximum Allowable Current for Various
Current-to-ADuM1200/ADuM1201 Spacings
Note that, at combinations of strong magnetic fields and high
frequencies, any loops formed by PCB traces can induce suffi-
ciently large error voltages to trigger the threshold of succeeding
circuitry. Take care in the layout of such traces to avoid this
possibility.
POWER CONSUMPTION
The supply current at a given channel of the ADuM1200/
ADuM1201 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
supply currents, the supply
currents for each input and output channel corresponding to
I
DD1
and I
DD2
are calculated and totaled. 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 11 provide total
V
DD1
and V
DD2
supply current as a function of data rate for
ADuM1200 and ADuM1201 channel configurations.