ADuM3151/ADuM3152/ADuM3153 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 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, it reduces the received pulse from >1.0 V to
0.75 V, which 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
ADuM3151/ADuM3152/ADuM3153 transformers. Figure 18
expresses these allowable current magnitudes as a function of
frequency for selected distances. The ADuM3151/ADuM3152/
ADuM3153 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, a user would have to
place a 1.2 kA current 5mm away from the ADuM3151/
ADuM3152/ADuM3153 to affect 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
12368-018
Figure 18. Maximum Allowable Current for Various Current to
ADuM3151/ADuM3152/ADuM3153 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 ADuM3151/
ADuM3152/ADuM3153 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 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 ADuM3151/ADuM3152/ADuM3153
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.
There are two types of insulation degradation 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.
Surface Tracking
Surface tracking is addressed in electrical safety standards by
setting a minimum surface creepage based on the working
voltage, the environmental conditions, and the properties of the
insulation material. Safety agencies perform characterization
testing on the surface insulation of components that allow the
components to be categorized into different material groups.
Lower material group ratings are more resistant to surface
tracking and, therefore, can provide adequate lifetime with
smaller creepage. The minimum creepage for a given working
voltage and material group is in each system level standard and
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