Data Sheet
ADuM7240/ADuM7241
1000
100
10
Note that with extreme combinations of strong magnetic field
and high frequency current, loops formed by printed circuit
board traces can induce error voltages large enough to trigger
the thresholds of receiver circuitry. Care should be taken in the
layout of such traces to avoid this possibility.
POWER CONSUMPTION
1
The supply current at a given channel of the ADuM7240/
ADuM7241 isolator is a function of the supply voltage, the
data rate of the channel, and the output load of the channel.
0.1
0.01
For each input channel, the supply current is given by
I
DDI = IDDI(Q)
f ≤ 0.5 fr
f > 0.5 fr
0.001
1k
10k
100k
1M
10M
100M
MAGNETIC FIELD FREQUENCY (Hz)
IDDI = IDDI(D) × (2f − fr) + IDDI(Q)
Figure 14. Maximum Allowable External Magnetic Flux Density
For each output channel, the supply current is given by
DDO = IDDO(Q) f ≤ 0.5 fr
DDO = (IDDO(D) + (0.5 × 10−3) × CL × VDDO) × (2f − fr) + IDDO(Q)
f > 0.5 fr
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. Similarly, if such an event occurs during a transmit-
ted pulse (and is of 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.
I
I
where:
DDI(D), IDDO(D) are the input and output dynamic supply currents
per channel (mA/Mbps).
I
CL is the output load capacitance (pF).
V
DDO is the output supply voltage (V).
The preceding magnetic flux density values correspond to
specific current magnitudes at given distances from the
ADuM7240/ADuM7241 transformers. Figure 15 shows these
allowable current magnitudes as a function of frequency for
selected distances. As shown in Figure 15, the ADuM7240/
ADuM7241 is 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, a 1.2 kA current
placed 5 mm away from the ADuM7240/ADuM7241 is
required to affect the operation of the component.
1000
f is the input logic signal frequency (MHz); it is half the input
data rate, expressed in units of 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
V
show per-channel supply currents as a function of data rate for
an unloaded output condition. Figure 8 shows the per-channel
supply current as a function of data rate for a 15 pF output
condition. Figure 9 through Figure 12 show the total VDD1 and
DD1 and VDD2 are calculated and totaled. Figure 6 and Figure 7
100
10
1
V
DD2 supply current as a function of data rate for ADuM7240
and ADuM7241 channel configurations.
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. 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 ADuM7240/
ADuM7241.
0.1
DISTANCE = 5mm
DISTANCE = 100mm
DISTANCE = 1m
0.01
1k
10k
100k
1M
10M
100M
MAGNETIC FIELD FREQUENCY (Hz)
Figure 15. Maximum Allowable Current for Various
Current-to-ADuM7240/ADuM7241 Spacings
Analog Devices performs accelerated life testing using voltage
levels higher than the rated continuous working voltage. Accelera-
tion 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 summa-
rize the working voltage for 50 years of service life.
Rev. A | Page 13 of 16
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