ADUM3470 AD [Analog Devices], ADUM3470 Datasheet - Page 31

• Manufacturer Part Number: ADUM3470
• Description: PWM Controller and Transformer Driver with Quad-Channel Isolators
• Manufacturer: AD [Analog Devices]

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 ADuM347x. Accelerated life
testing is performed using voltage levels higher than the rated
continuous working voltage. Acceleration factors for several
operating conditions are determined, allowing calculation 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 ADuM347x depends on the voltage
waveform type imposed across the isolation barrier. The i Coupler
insulation structure degrades at different rates, depending on
whether the waveform is bipolar ac, dc, or unipolar ac. Figure 46,
Figure 47, and Figure 48 illustrate these different isolation voltage
waveforms.
CC
, the primary side converter
ADuM3470/ADuM3471/ADuM3472/ADuM3473/ADuM3474
Rev. 0 | Page 31 of 32
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 that the voltage conforms to
either the unipolar ac or dc voltage cases. Treat any cross-
insulation voltage waveform that does not conform to Figure 47 or
Figure 48 as a bipolar ac waveform, and limit its peak voltage to
the 50-year lifetime voltage value listed in Table 11.
RATED PEAK VOLTAGE
NOTES:
0V
1. THE VOLTAGE IS SHOWN SINUSOIDAL
FOR ILLUSTRATION PURPOSES ONLY.
IT IS MEANT TO REPRESENT ANY VOLRTAGE
WAVEFORM VARYING BETWEEN 0 AND SOME
LIMITING VALUE. THE LIMITING VALUE CAN BE
POSTIVE OR NEGATIVE, BUT THE VOLTAGE
CANNOT CROSS 0V.
RATED PEAK VOLTAGE
RATED PEAK VOLTAGE
0V
0V
Figure 48. Unipolar AC Waveform
Figure 46. Bipolar AC Waveform
Figure 47. DC Waveform