adum5401w Analog Devices, Inc., adum5401w Datasheet - Page 18

• Manufacturer Part Number: adum5401w
• Description: Quad-channel Isolators With Integrated Dc-to-dc Converter
• Manufacturer: Analog Devices, Inc.

ADuM5401W/ADuM5402W/ADuM5403W
When the primary side is above the UVLO threshold, the data
input channels sample their inputs and begin sending encoded
pulses to the inactive secondary output channels. The outputs
on the primary side remain in their default low state because no
data comes from the secondary side inputs until secondary power
is established. The primary side oscillator also begins to operate,
transferring power to the secondary power circuits. The secondary
V
control signal from the secondary is not being generated. The
primary side power oscillator is allowed to free run in this
circumstance, supplying the maximum amount of power to
the secondary, until the secondary voltage rises to its regulation
setpoint. This creates a large inrush current transient at V
When the regulation point is reached, the regulation control
circuit produces the regulation control signal that modulates
the oscillator on the primary side. The V
and is then proportional to the load current. The inrush current
is less than the short-circuit current shown in Figure 12. The
duration of the inrush depends on the V
and the current available at the V
As the secondary side converter begins to accept power from
the primary, the V
side UVLO is reached, the secondary side outputs are initialized to
their default low state until data is received from the corresponding
primary side input. It can take up to 1 μs after the secondary side is
initialized for the state of the output to correlate with the primary
side input.
Secondary side inputs sample their state and transmit it to the
primary side. Outputs are valid about 1 μs after the secondary
side becomes active.
Because the rate of charge of the secondary side power supply is
dependent on loading conditions, the input voltage, and the output
voltage level selected, take care with the design to allow the
converter sufficient time to stabilize before valid data is required.
When power is removed from V
and coupler shut down when the UVLO level is reached. The
secondary side stops receiving power and starts to discharge.
The outputs on the secondary side hold the last state that they
received from the primary side. Either the UVLO level is reached
and the outputs are placed in their high impedance state, or the
outputs detect a lack of activity from the primary side inputs
and the outputs are set to their default low value before the
secondary power reaches UVLO.
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. Analog Devices conducts
an extensive set of evaluations to determine the lifetime of the
insulation structure within the ADuM5401W/ADuM5402W/
ADuM5403W.
ISO
voltage is below its UVLO limit at this point; the regulation
ISO
voltage starts to rise. When the secondary
DD1
DD1
pin.
, the primary side converter
ISO
DD1
loading conditions
current is reduced
DD1
.
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Accelerated life testing is performed using voltage levels higher
than the rated continuous working voltage. Acceleration factors
for several operating conditions are determined, allowing calcu-
lation of the time to failure at the working voltage of interest.
The values shown in Table 11 summarize the peak voltages for
50 years of service life in several operating conditions. In many
cases, the working voltage approved by agency testing is higher
than the 50-year service life voltage. Operation at working
voltages higher than the service life voltage listed leads to
premature insulation failure.
The insulation lifetime of the ADuM5401W/ADuM5402W/
ADuM5403W 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 25, Figure 26, and Figure 27
illustrate these different isolation voltage waveforms.
Bipolar ac voltage is the most stringent environment. 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 11 can be applied while maintaining the
50-year minimum lifetime, provided the voltage conforms to
either the unipolar ac or dc voltage cases. Any cross-insulation
voltage waveform that does not conform to Figure 26 or Figure 27
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 11.
NOTES
1. THE VOLTAGE IS SHOWN AS SINUSOIDAL FOR ILLUSTRATION
PURPOSES ONLY. IT IS MEANT TO REPRESENT ANY VOLTAGE
WAVEFORM VARYING BETWEEN 0 AND SOME LIMITING VALUE.
THE LIMITING VALUE CAN BE POSITIVE OR NEGATIVE, BUT THE
VOLTAGE CANNOT CROSS 0V.
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
0V
0V
0V
Figure 27. Unipolar AC Waveform
Figure 25. Bipolar AC Waveform
Figure 26. DC Waveform