ADuM4151/ADuM4152/ADuM4153 Data Sheet
For example, at a magnetic field frequency of 1 MHz, the
maximum allowable magnetic field of 0.5 kgauss, induces a
voltage of 0.25 V at the receiving coil. This voltage is about 50%
of the sensing threshold and does not cause a faulty output
transition. If such an event occurs, with the worst-case polarity,
during a transmitted pulse, the interference reduces the
received pulse from >1.0 V to 0.75 V. This voltage is 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
ADuM4151/ADuM4152/ADuM4153 transformers. Figure 18
expresses these allowable current magnitudes as a function of
frequency for selected distances. The ADuM4151/ADuM4152/
ADuM4153 are insensitive to external fields. Only extremely
large, high frequency currents, very close to the component are
a concern. For the 1 MHz example noted, placing a 1.2 kA
current 5 mm away from the ADuM4151/ADuM4152/
ADuM4153 affects component 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
12370-018
Figure 18. Maximum Allowable Current for Various Current to
ADuM4151/ADuM4152/ADuM4153 Spacings
At combinations of strong magnetic field and high frequency,
any loops formed by the PCB traces may induce sufficiently
large error voltages to trigger the thresholds of succeeding
circuitry. Take care to avoid PCB structures that form loops.
POWER CONSUMPTION
The supply current at a given channel of the ADuM4151/
ADuM4152/ADuM4153 isolators is a function of the supply
voltage, the data rate of the channel, and the output load of the
channel and whether it is a high or low speed channel.
The low speed channels draw a constant quiescent current
caused by the internal ping-pong datapath. The operating
frequency is low enough that the capacitive losses caused by
the recommended capacitive load are negligible compared to
the quiescent current. The explicit calculation for the data rate
is eliminated for simplicity, and the quiescent current for each
side of the isolator due to the low speed channels can be found
in Table 3, Table 6, Table 9, and Table 12 for the particular
operating voltages.
These quiescent currents add to the high speed current as is
shown in the following equations for the total current for each
side of the isolator. Dynamic currents are taken from Table 3
and Table 6 for the respective voltages.
For Side 1, the supply current is given by
I
DD1
= I
DDI(D)
× (f
MCLK
+ f
MO
+ f
MSS
) +
f
MI
× (I
DDO(D)
+ ((0.5 × 10
−3
) × C
L(MI)
× V
DD1
)) + I
DD1(Q)
For Side 2, the supply current is given by
I
DD2
= I
DDI(D)
× f
SO
+
f
SCLK
× (I
DDO(D)
+((0.5 × 10
−3
) × C
L(SCLK)
× V
DD2
)) +
f
SI
× (I
DDO(D)
+((0.5 × 10
−3
) × C
L(SI)
× V
DD2
)) +
f
SSS
× (I
DDO(D)
+((0.5 × 10
−3
) × C
L(
SSS
)
× V
DD2
)) + I
DD2(Q)
where:
I
DDI(D)
, I
DDO(D)
are the input and output dynamic supply currents
per channel (mA/Mbps).
f
x
is the logic signal data rate for the specified channel (Mbps).
C
L(x)
is the load capacitance of the specified output (pF).
V
DDx
is the supply voltage of the side being evaluated (V).
I
DD1(Q)
, I
DD2(Q)
are the specified Side 1 and Side 2 quiescent
supply currents (mA).
Figure 8 and Figure 11 show the typical supply current per
channel as a function of data rate for an input and unloaded
output. Figure 9 and Figure 12 show the total I
DD1
and I
DD2
supply
currents as a function of data rate for the ADuM4151/ADuM4152/
ADuM4153 channel configurations with all high speed channels
running at the same speed and the low speed channels at idle.
INSULATION LIFETIME
All insulation structures eventually break down when subjected
to voltage stress over a sufficiently long period. The rate of
insulation degradation is dependent on the characteristics of the
voltage waveform applied across the insulation as well as the
materials and material interfaces.
Two types of insulation degradation are of primary interest:
breakdown along surfaces exposed to the air and insulation
wear out. Surface breakdown is the phenomenon of surface
tracking and the primary determinant of surface creepage
requirements in system level standards. Insulation wear out is
the phenomenon where charge injection or displacement
currents inside the insulation material cause long-term
insulation degradation.
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