Data Sheet ADuM7640/ADuM7641/ADuM7642/ADuM7643
Rev. 0 | Page 19 of 20
POWER CONSUMPTION
The supply current at a given channel of the ADuM7640/
ADuM7641/ADuM7642/ADuM7643 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
I
DDI
= I
DDI (Q)
f ≤ 0.5 f
r
I
DDI
= I
DDI (D)
× (2f − f
r
) + I
DDI (Q)
f > 0.5 f
r
For each output channel, the supply current is given by
I
DDO
= I
DDO (Q)
f ≤ 0.5 f
r
I
DDO
= (I
DDO (D)
+ (0.5 × 10
−3
) × C
L
× V
DDO
) × (2f − f
r
) + I
DDO (Q)
f > 0.5 f
r
where:
I
DDI (D)
, I
DDO (D)
are the input and output dynamic supply currents
per channel (mA/Mbps).
I
DDI (Q)
, I
DDO (Q)
are the specified input and output quiescent
supply currents (mA).
f is the input logic signal frequency (MHz); it is half the input
data rate, expressed in units of Mbps.
f
r
is the input stage refresh rate (Mbps).
C
L
is the output load capacitance (pF).
V
DDO
is the output supply voltage (V).
To calculate the total V
DD1
and V
DD2
supply current, the supply
currents for each input and output channel corresponding to
V
DD1
and V
DD2
are calculated and totaled. Figure 10 and Figure 11
show per-channel supply currents as a function of data rate for
an unloaded output condition. Figure 12 shows the per-channel
supply current as a function of data rate for a 15 pF output
condition. Figure 13 through Figure 17 show the total V
DD1
and
V
DD2
supply current as a function of data rate for ADuM7640/
ADuM7641/ADuM7642/ADuM7643 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 depends 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 ADuM7640/ADuM7641/ADuM7642/
ADuM7643 components.
Analog Devices performs accelerated life testing using voltage
levels higher than the rated continuous working voltage. Accel-
eration 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 working voltages. In many cases,
the approved working voltage is higher than the 50-year service life
voltage. Operation at these high working voltages can lead to
shortened insulation life in some cases.
The insulation lifetime of the ADuM7640/ADuM7641
/
ADuM7642/ADuM7643 depends on the voltage waveform type
imposed across the isolation barrier. The iCoupler insulation
structure degrades at different rates depending on whether the
waveform is bipolar ac, unipolar ac, or dc. Figure 24, Figure 25,
and Figure 26 illustrate these different isolation voltage
waveforms.
Bipolar ac voltage is the most stringent environment. The goal
of a 50-year operating lifetime under the bipolar ac condition
determines the Analog Devices recommended maximum
working voltage.
In the case of unipolar ac or dc voltage, the stress on the insulation
is significantly lower. This allows operation at higher working
voltages while still achieving a 50-year service life. The working
voltages listed in Table 18 can be applied while maintaining the
50-year minimum lifetime, provided that the voltage conforms to
either the unipolar ac or dc voltage case. Any cross-insulation
voltage waveform that does not conform to Figure 25 or Figure 26
should be treated as a bipolar ac waveform, and its peak voltage
should be limited to the 50-year lifetime voltage value listed in
Table 18.
The voltage presented in Figure 25 is shown as sinusoidal for
illustration purposes only. It is meant to represent any voltage
waveform varying between 0 V and some limiting value. The
limiting value can be positive or negative, but the voltage cannot
cross 0 V.
0V
RATED PEAK VOLTAGE
10448-024
Figure 24. Bipolar AC Waveform
0V
RATED PEAK VOLTAGE
10448-025
Figure 25. Unipolar AC Waveform
0V
RATED PEAK VOLTAGE
10448-026
Figure 26. DC Waveform
