Data Sheet ADuM5240/ADuM5241/ADuM5242
Rev. B | Page 13 of 16
Load regulation transients are the primary source of lower
frequency power supply voltage excursions, as illustrated in
Figure 10. These should be dealt with by adding an additional
supply stiffening capacitor between V
ISO
and GND
ISO
. The
stiffening capacitor can be of a more highly inductive type
because the high frequency bypass is handled by the required
low inductance capacitor.
06014-015
V
DD
IA/OA
IB/OB
GND
V
ISO
V
OA/IA
V
OB/IB
GND
ISO
100nF
100nF
OPT
Figure 15. Recommended Printed Circuit Board Layout
In applications involving high common-mode transients, care
should be taken to ensure that board coupling across the isolation
barrier is minimized. Furthermore, the board layout should be
designed such that any coupling that does occur equally affects
all pins on a given component side. Failure to ensure this can
cause voltage differentials between pins exceeding the absolute
maximum ratings of the device (specified in Table 7), thereby
leading to latch-up and/or permanent damage.
The ADuM524x is a power device that dissipates as much as
600 mW of power when fully loaded. Because it is not possible
to apply a heat sink to an isolation device, the device primarily
depends on heat dissipation into the PCB through the GND
pins. If the device is used at high ambient temperatures, care
should be taken to provide a thermal path from the GND pins
to the PCB ground plane. The board layout in Figure 15 shows
enlarged pads for Pin 4 and Pin 5. Multiple vias should be
implemented from each of the pads to the ground plane,
which significantly reduce the temperatures inside the chip.
The dimensions of the expanded pads are left to the discretion
of the designer and the available board space.
INCREASING AVAILABLE POWER
The ADuM524x devices are not designed with the capability of
running several devices in parallel. However, if more power is
required to run multiple loads, it is possible to group loads and
run each group from an individual ADuM542x device. For
example, if a transceiver and external logic must be powered,
one ADuM524x could be dedicated to the transceiver and an
additional ADuM524x could power the external logic, which
prevents issues with load sharing because each load is dedicated
to its own supply.
INSULATION LIFETIME
All insulation structures eventually breaks 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. 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 ADuM524x.
Analog Devices performs accelerated life testing using voltage
levels higher than the rated continuous working voltage. Accel-
eration 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 8 summarize the peak
voltage for 50 years of service life for a bipolar ac operating condi-
tion and the maximum CSA/VDE approved working voltages. In
many cases, the approved working voltage is higher than 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 ADuM524x 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 16,
Figure 17, and Figure 18 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 recommended maximum working voltage of
Analog Devices.
In the case of unipolar ac or dc voltage, the stress on the
insulation is significantly lower, which allows operation at
higher working voltages while still achieving a 50-year service
life. The working voltages listed in Table 8 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 17 or
Figure 18 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 8.
Note that the voltage presented in Figure 17 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
06014-021
Figure 16. Bipolar AC Waveform
0V
RATED PEAK VOLTAGE
06014-022
Figure 17. Unipolar AC Waveform
0V
RATED PEAK VOLTAGE
06014-023
Figure 18. DC Waveform
