ADDC02808PB(Rev0) View Datasheet(PDF) - Analog Devices
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Description
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ADDC02808PB Datasheet PDF : 20 Pages
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ADDC02808PB
RS101: This requirement is specialized and is intended to check 3. A repetitively pulsed load will cause large input currents at
for sensitivity to low frequency magnetic fields in the 30 Hz to
the fundamental frequency (and harmonics) of the pulse
50 kHz range. The converter is designed to meet this require-
waveform.
ment. Consult factory for more information.
The result of Items 1 and 2 is that the ADDC02808PB
RS103: This test calls for correct operation during and after the converter will have higher conducted and radiated emissions in
unit under test is subjected to radiated electric fields in the 10 kHz the 1/2 MHz to 10 MHz range. The emissions in this range are
to 40 GHz range. The intent is to simulate electromagnetic
dominated by differential currents. These currents are
fields generated by antenna transmissions. The converter is
proportional to power, so we would expect a factor of two
designed to meet this requirement. Consult factory for more
increase in emissions due to the 200 W operating level. It does
information.
not matter that the average power of this pulsed unit is 100 W
Circuit Setup for EMI Test
or lower. MIL-STD-462D calls for measurements to be made
Figure 15 shows a schematic of the test setup used for the EMI with peak detectors that will determine the emissions during the
measurements discussed above. The output of the converter is
200 W pulse, and not average them in any way with the lower
OBSOLETE connected to a resistive load designed to draw full power. There
is a 0.1 µF capacitor placed across this resistor that typifies by-
pass capacitance normally used in this application. At the input
of the converter there are two differential capacitors (the larger
one having a series resistance) and two small common-mode
capacitors connected to case ground. The case itself was con-
nected to the metal ground plane in the test chamber. For the
RE102 test, a metal screen box was used to cover both the
converter and its load (but not the two meters of input power
lead cables). This box was also electrically connected to the
metal ground plane.
With regard to the components added to the input power lines,
the 100 µF capacitor with its 1 Ω series resistance is required to
achieve system stability when the unit is powered through the
LISNs, as the MIL-STD-461D standard requires. These
LISNs have a series inductance of 50 µH at low frequencies,
giving a total differential inductance of 100 µH. As explained
power part of the cycle.
In addition, the differential EMI filter in the ADDC02808PB
converter is less effective at attenuating the ripple currents than
is the filter in the ADDC02805SA converter due to smaller
value inductors. Figure 38 shows the transfer functions of these
two filters in the frequency range of interest.
Combining the factor of two and the reduced filter attenuation,
Figure 39 shows the ratio, in dB, by which the emissions of
Figures 12 and 14 should be increased to estimate the emissions
of the ADDC02808PB converter in this frequency range. From
this curve the 1/2 MHz component should increase by 25 dB,
and the 1 MHz and higher components should increase by 22 dB.
For both conducted and radiated tests, this increase would
require some additional differential filtering to meet the most
stringent MIL-STD-461D levels shown in the figures. This
could be done, for example, by increasing the 2 µF ceramic (low
parasitic inductance) capacitor placed across the input of the
earlier in the System Instability section, such a large series
converter in Figure 15 to 30 µF or, a small 0.5 µH, 16 A
source inductance will cause an instability as it interacts with the inductor could be placed in series between the top of the 2 µF
converter’s negative incremental input resistance unless some
corrective action is taken. The 100 µF capacitor and 1 Ω
capacitor and the +VIN pin. Figures 40 and 41 show the ratios,
resistor provide the stabilization required.
100
It should be noted that the values of these stabilization components
are appropriate for a single converter load. If the system makes
use of several converters, the values of the components will need
to be changed slightly, but not such that they are repeated for
every converter. It should also be noted that most system
applications will not have a source inductance as large as the
100 µH built into the LISNs. For those systems, a much
smaller input capacitor could be used.
The 2 µF differential-mode capacitor and the two 82 nF
common-mode capacitors were added to achieve the results
shown in the EMI measurement figures described above.
ADDC02808PB EMI Performance
The EMI performance of the ADDC02808PB power converter
will be different from the ADDC02805SA baseline previously
discussed for several reasons:
1. Its maximum power is 200 W, or twice that of the
ADDC02805SA converter.
10
1
0.1
0.01
0.001
10–4
10–5
10–6
10–7
10–8
1•104
ADDC02808PB
ADDC02805SA
1•105
1•106
FREQUENCY – Hz
1•107
Figure 38. Comparison of Transfer Functions for the Input
EMI Filters in ADDC02805SA and ADDC02808PB
2. Its differential input filter inductors are smaller in value by a
factor of two compared to those in the ADDC02805SA
converter to accommodate input stability at the higher power
level.
REV. 0
–17–
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