adum5401 Analog Devices, Inc., adum5401 Datasheet - Page 20

• Manufacturer Part Number: adum5401
• Description: Quad-channel Isolators With Integrated Dc-to-dc Converter
• Manufacturer: Analog Devices, Inc.

ADuM5401/ADuM5402/ADuM5403/ADuM5404
POWER CONSIDERATIONS
The ADuM5401/ADuM5402/ADuM5403/ADuM5404 power
input, the data input channels on the primary side, and the data
input channels on the secondary side are all protected from
premature operation by UVLO circuitry. Below the minimum
operating voltage, the power converter holds its oscillator inactive,
and all input channel drivers and refresh circuits are idle. Outputs
are held in a low state. This is to prevent transmission of
undefined states during power-up and power-down operations.
During application of power to V
is held idle until the UVLO preset voltage is reached. At that time,
the data channels are initialized to their default low output state
until they receive data pulses from the secondary side.
The primary side input channels sample the input and send a pulse
to the inactive secondary output. The secondary side converter
begins to accept power from the primary, and the V
starts to rise. When the secondary side UVLO is reached, the
secondary side outputs are initialized to their default low state
until data, either a transition or a dc refresh pulse, 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 one propagation delay after the
secondary side becomes active.
Because the rate of charge of the secondary side is dependent
on loading conditions, input voltage, and output voltage level
selected, care should be taken in the design to allow the converter
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 until either the UVLO level is reached
and the outputs are placed in their default low state, or the outputs
detect a lack of activity from the inputs and the outputs are set
to their default 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 insu-
lation 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 ADuM5401/ADuM5402/
ADuM5403/ADuM5404.
Accelerated life testing is performed using voltage levels higher
than the rated continuous working voltage. Acceleration factors
DD1
DD1
, the primary side converter
, the primary side circuitry
ISO
voltage
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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 9 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 ADuM5401/ADuM5402/
ADuM5403/ ADuM5404 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 28, Figure 29,
and Figure 30 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 9 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 29 or Figure 30
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 9.
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
0V
0V
RATED PEAK VOLTAGE
0V
Figure 30. Unipolar AC Waveform
Figure 28. Bipolar AC Waveform
Figure 29. DC Waveform