adum7440 Analog Devices, Inc., adum7440 Datasheet - Page 15

• Manufacturer Part Number: adum7440
• Description: 1 Kv Rms Quad-channel Digital Isolators
• Manufacturer: Analog Devices, Inc.

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
ADuM744x transformers. Figure 19 shows these allowable
current magnitudes as a function of frequency for selected
distances. As shown, the ADuM744x 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 noted previously, a 1.2 kA current would have to be
placed 5 mm away from the ADuM744x to affect the operation
of the component.
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. Care should be taken in the
layout of such traces to avoid this possibility.
0.001
Figure 18. Maximum Allowable External Magnetic Flux Density
1000
1000
0.01
0.01
100
100
0.1
0.1
10
10
1
1
1k
1k
Figure 19. Maximum Allowable Current for Various
DISTANCE = 5mm
DISTANCE = 100mm
DISTANCE = 1m
10k
10k
Current-to-ADuM744x Spacings
MAGNETIC FIELD FREQUENCY (Hz)
MAGNETIC FIELD FREQUENCY (Hz)
100k
100k
1M
1M
10M
10M
100M
100M
Rev. 0 | Page 15 of 20
POWER CONSUMPTION
The supply current at a given channel of the ADuM744x
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
For each output channel, the supply current is given by
where:
I
per channel (mA/Mbps).
C
V
f is the input logic signal frequency (MHz); it is half the input
data rate, expressed in units of Mbps.
f
I
supply currents (mA).
To calculate the total V
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 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 V
V
ADuM7441/ADuM7442 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 ADuM744x.
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 17 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.
r
DDI (D)
DDI (Q)
L
DDO
is the input stage refresh rate (Mbps).
DD1
DD2
is the output load capacitance (pF).
I
I
I
I
and V
supply current as a function of data rate for ADuM7440/
is the output supply voltage (V).
DDI
DDI
DDO
DDO
, I
, I
DDO (D)
DDO (Q)
= I
= I
= (I
= I
ADuM7440/ADuM7441/ADuM7442
DD2
DDI (D)
DDI (Q)
DDO (Q)
DDO (D)
are the input and output dynamic supply currents
are the specified input and output quiescent
are calculated and totaled. Figure 8 and Figure 9
× (2f − f
+ (0.5 × 10
DD1
r
) + I
and V
−3
DDI (Q)
) × C
DD2
L
supply current, the supply
× V
DDO
) × (2f − f
r
f ≤ 0.5 f
f > 0.5 f
f ≤ 0.5 f
f > 0.5 f
) + I
DD1
DDO (Q)
and
r
r
r
r