Data Sheet ADuM3480/ADuM3481/ADuM3482
Rev. A | Page 19 of 20
Calculating I
DDL1
or I
DDL2
For each input channel, the supply current is given by
I
DDIL
= I
DDIL (D)
× R
D
+ I
DDIL (Q)
For each output channel, the supply current is given by
)(
3
)(
2
10
QDDOLD
DDOLL
DDDOLDDOL
IR
VC
II +
××
+=
−
where:
C
L
is the output load capacitance (pF).
V
DDOL
is the output supply voltage (V).
R
D
is the input logic signal data rate (Mbps); it is twice the input
frequency, expressed in units of MHz.
R
R
is the input stage refresh rate (Mbps) = 1/t
r
(µs)
I
DDI (Q)
, I
DDIL (Q)
, I
DDO (Q)
, I
DDOL (Q)
are the specified input and output
quiescent supply currents (mA).
I
DDI (D)
, I
DDIL (D)
, I
DDO (D)
, and I
DDOL(D)
are the input and output
dynamic supply currents per channel (mA/Mbps).
As inputs and outputs can be present on each side of the device,
the calculations refer to the current drawn from the local supply.
For example, if an output is on Side 2 of a part, the I
DDOL
current
is drawn from the V
DDL2
pin of the part. The I
DDL1
and I
DDL2
currents
are dependent on V
DDL1
and V
DDL2
, the data rate, and the capacitive
load. It is nearly independent of the value of the core supplies.
To calculate the total I
DD1
, I
DDL1
, I
DD2
, and I
DDL2
supply current, the
supply currents for each input and output channel corresponding to
V
DD1
, V
DDL1
, V
DD2
, and V
DDL2
are calculated and totaled, or read from
Figure 8 through Figure 14.
The input current for the regulated core power supplies is
nearly independent of the I/O voltage, and scales with data rate.
The I
DDI
current is not linear down to dc, but goes to a minimum
value between about 2.5 × R
R
and dc. This is due to the refresh
circuit establishing a minimum data rate; the values in Figure 8 and
Figure 9 and the quiescent currents in Table 3, Table 6, and Table 9
approximate the current in this region. V
DDI
, V
DDO
, V
DDIL
, and
V
DDOL
represent the voltages on the core and I/O power supply
pins for the input and output of a given channel. I represents an
input, O is an output, and L denotes an I/O supply.
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 ADuM3480/ADuM3481/ADuM3482.
Analog Devices performs accelerated life testing using voltage
levels that are 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 16 summarize the
peak voltage for 50 years of service life for a bipolar ac operating
condition and the maximum CSA/VDE approved 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
ADuM3480/ADuM3481/ADuM3482 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 19,
Figure 20,and Figure 21 illustrate these different isolation
voltage waveforms.
Bipolar ac voltage is the most stringent environment. The goal
of a 50-year operating lifetime under the ac bipolar condition
determines the maximum working voltage recommended by
Analog Devices.
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 16 can be applied while maintaining the
50-year minimum lifetime, provided that the voltage conforms to
either the unipolar ac or dc voltage case. Treat any cross-insulation
voltage waveform that does not conform to Figure 19, Figure 20,
or Figure 21 as a bipolar ac waveform, and limit its peak voltage
to the 50-year lifetime voltage value listed in Table 16.
Note that the voltage presented in Figure 20 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
10459-020
Figure 19. Bipolar AC Waveform
0V
RATED PEAK VOLTAGE
10459-021
Figure 20. Unipolar AC Waveform
0V
RATED PEAK VOLTAGE
10459-023
Figure 21. DC Waveform
