Data Sheet ADuM7440/ADuM7441/ADuM7442
Rev. D | Page 15 of 20
MAXIMUM ALLOWABLE MAGNETIC FLUX (kgauss)
MAGNETIC FIELD FREQUENCY(Hz)
Figure 18. Maximum Allowable External Magnetic Flux Density
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.
Similarly, if such an event occurred 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
ADuM7440/ADuM7441/ADuM7442 transformers. Figure 19
shows these allowable current magnitudes as a function of
frequency for selected distances. As shown, the ADuM7440/
ADuM7441/ADuM7442 are 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 previously, a 1.2 kA current would have to be placed
5 mm away from the ADuM7440/ADuM7441/ADuM7442 to
affect the operation of the component.
MAXIMUM ALLOWABLE CURRENT (kA)
100k 1M 10M
MAGNETIC FIELD FREQUENCY (Hz)
DISTANCE = 5mm
DISTANCE = 100mm
DISTANCE = 1m
Figure 19. Maximum Allowable Current for Various
Note that at combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board traces can
induce error voltages sufficiently large enough to trigger the
thresholds of succeeding circuitry. Take care in the layout of
such traces to avoid this possibility.
The supply current at a given channel of the ADuM7440/
ADuM7441/ADuM7442 isolator is a function of the supply
voltage, the data rate of the channel, and the output load of the
For each input channel, the supply current is given by
IDDI = IDDI (Q) f ≤ 0.5 fr
IDDI = IDDI (D) × (2f − fr) + IDDI (Q) f > 0.5 fr
For each output channel, the supply current is given by
IDDO = IDDO (Q) f ≤ 0.5 fr
IDDO = (IDDO (D) + (0.5 × 10−3) × CL × VDDO) × (2f − fr) + IDDO (Q)
f > 0.5 fr
IDDI (D), IDDO (D) are the input and output dynamic supply currents
per channel (mA/Mbps).
CL is the output load capacitance (pF).
VDDO is the output supply voltage (V).
f is the input logic signal frequency (MHz); it is half the input
data rate, expressed in Mbps.
fr is the input stage refresh rate (Mbps).
IDDI (Q), IDDO (Q) are the specified input and output quiescent
supply currents (mA).
To calculate the total VDD1 and VDD2 supply current, the supply
currents for each input and output channel corresponding to
VDD1 and VDD2 are calculated and totaled. Figure 8 and Figure 9
show per-channel supply currents as a function of data rate for
an unloaded output condition. Figure 10 shows the per-channel
supply current as a function of data rate for a 15 pF output
condition. Figure 11 through Figure 15 show the total VDD1 and
VDD2 supply current as a function of data rate for ADuM7440/
ADuM7441/ADuM7442 channel configurations.
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. In addition to
the testing performed by the regulatory agencies, Analog Devices
carries out an extensive set of evaluations to determine the
lifetime of the insulation structure within the ADuM7440/
Analog Devices performs accelerated life testing using voltage
levels higher than the rated continuous working voltage.
Acceleration factors for several operating conditions are
determined. These factors allow calculation of the time to
failure at the actual working voltage. The values shown in
Table 18 summarize the peak voltage for 50 years of service life
for a bipolar ac operating condition and the maximum CSA
approved working voltages. In many cases, the approved working
voltage is higher than 50-year service life voltage. Operation at
these high working voltages can lead to shortened insulation life
in some cases.