ADUM3070 AD [Analog Devices], ADUM3070 Datasheet - Page 18

• Manufacturer Part Number: ADUM3070
• Description: Isolated Switching Regulator
• Manufacturer: AD [Analog Devices]

ADuM3070
POWER CONSIDERATIONS
Soft Start Mode and Current-Limit Protection
When the
in soft start mode, and the output voltage, V
gradually while it is below the startup threshold. In soft start
mode, to limit the peak current during V
primary converter gradually increases the width of the PWM
signal. When the output voltage is larger than the start-up
threshold, the PWM signal can be transferred from the secondary
controller to the primary converter, and the dc-to-dc converter
switches from soft start mode to the normal PWM control mode.
If a short circuit occurs, the push-pull converter shuts down for
about 2 ms and then enters soft start mode. If, at the end of soft
start, a short circuit still exists, the process is repeated, which is
called hiccup mode. If the short circuit is cleared, the
enters normal operation.
The
active at startup and during normal operation, that protects the
primary switches, X1 and X2, from exceeding approximately
1.3 A peak, protecting the transformer windings.
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, Inc.,
conducts an extensive set of evaluations to determine the lifetime of
the insulation structure within the ADuM3070. 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.
ADuM3070
ADuM3070
has a pulse-by-pulse current limit, which is
first receives power from V
ISO
power-up, the
ISO
, is increased
DD1
ADuM3070
, it is
Rev. 0 | Page 18 of 20
The insulation lifetime of the
waveform type imposed across the isolation barrier. The iCoupler
insulation structure degrades at different rates, depending on
whether the waveform is bipolar ac, dc, or unipolar ac. Figure 36,
Figure 37, and Figure 38 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, if the voltage conforms to either the
unipolar ac or dc voltage cases. Treat any cross-insulation voltage
waveform that does not conform to Figure 37 or Figure 38 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
1. THE VOLTAGE IS SHOWN SINUSOIDAL
0V
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
Figure 38. Unipolar AC Waveform
Figure 36. Bipolar AC Waveform
Figure 37. DC Waveform
ADuM3070
depends on the voltage
Data Sheet