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參數資料
| 型號： | ADDC02828SATV |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | 28 V/100 W DC/DC Converter with Integral EMI Filter |
| 中文描述： | 2-OUTPUT 100 W DC-DC UNREG PWR SUPPLY MODULE |
| 封裝： | HERMETIC SEALED, HYBRID PACKAGE-17 |
| 文件頁數： | 11/16頁 |
| 文件大小： | 204K |
| 代理商： | ADDC02828SATV |
ADDC02828SA
REV. 0
–11–
For the power delivery to be efficient, it is required that R
S
<< R
N
.
For the system to be stable, however, the following relationship
must hold:
C
P
|
R
N
|
>
(
L
S
+
L
P
)
R
S
or
R
S
>
(
L
S
+
L
P
)
C
P
|
R
N
|
Notice from this result that if (L
S
+ L
P
) is too large, or if R
S
is
too small, the system might be unstable. T his condition would
first be observed at low input line and full load since the abso-
lute value of R
N
is smallest at this operating condition.
If an instability results, and it cannot be corrected by changing
L
S
or R
S
(such as during the MIL-ST D-461D tests) due to the
LISN requirement, one possible solution is to place a capacitor
across the input of the POL converter. Another possibility is to
place a small resistor in series with this extra capacitor.
T he analysis so far has assumed the source of power was a volt-
age source (e.g., a battery) with some source impedance. In
some cases, this source may be the output of a front-end (FE)
converter. Although each FE converter is different, a model for
a typical one would have an LC output filter driven by a voltage
source whose value was determined by the feedback loop. T he
L C filter usually has a high Q, so the compensation of the
feedback loop is chosen to help dampen any oscillations that
result from load transients. In effect, the feedback loop adds
“positive resistance” to the LC network.
When the POL converter is connected to the output of this FE
converter, the POL’s “negative resistance” counteracts the
effects of the FE’s “positive resistance” offered by the feedback
loop. Depending on the specific details, this might simply mean
that the FE converter’s transient response is slightly more oscil-
latory, or it may cause the entire system to be unstable.
For the ADDC02828SA, L
P
is approximately 1
μ
H and C
P
is
approximately 4
μ
F. Figure 8 shows a more accurate depiction
of the input impedance of the converter as a function of fre-
quency. T he negative resistance is, itself, a very good incremen-
tal model for the power state of the converter for frequencies
into the several kHz range.
NAVMAT DE RAT ING
NAVMAT is a Navy power supply reliability manual that is
frequently cited by specifiers of power supplies. A key section of
NAVMAT P4855-1A discusses guidelines for derating designs
and their components. T he two key derating criteria are voltage
derating and power derating. Voltage derating is done to reduce
the possibility of electrical breakdown, whereas power derating
is done to maintain the component material below a specified
maximum temperature. While power deratings are typically
stated in terms of current limits (e.g., derate to x% of maximum
rating), NAVMAT also specifies a maximum junction tem-
perature of the semiconductor devices in a power supply. T he
NAVMAT component deratings applicable to the ADDC02828SA
are as follows:
Resistors
80% voltage derating
50% power derating
Capacitors
50% voltage and ripple voltage derating
70% ripple current derating
T ransformers and Inductors
60% continuous voltage and current derating
90% surge voltage and current derating
20
°
C less than rated core temperature
30
°
C below insulation rating for hot spot temperature
25% insulation breakdown voltage derating
40
°
C maximum temperature rise
T ransistors
50% power derating
60% forward current (continuous) derating
75% voltage and transient peak voltage derating
110
°
C maximum junction temperature
Diodes (Switching, General Purpose, Rectifiers)
70% current (surge and continuous) derating
65% peak inverse voltage derating
110
°
C maximum junction temperature
Diodes (Zeners)
70% surge current derating
60% continuous current derating
50% power derating
110
°
C maximum junction temperature
Microcircuits (Linears)
70% continuous current derating
75% signal voltage derating
110
°
C maximum junction temperature
T he ADDC02828SA can meet all the derating criteria listed
above. However, there are a few areas of the NAVMAT deratings
where meeting the guidelines unduly sacrifices performance of
the circuit. T herefore, the standard unit makes the following
exceptions.
C ommon-Mode E MI F ilter C apacitors:
T he standard
supply uses 500 V capacitors to filter common-mode EMI.
NAVMAT guidelines would require 1000 V capacitors to meet
the 50% voltage derating (500 V dc input to output isolation),
resulting in less common-mode capacitance for the same space.
In typical electrical power supply systems, where the load
ground is eventually connected to the source ground, common-
mode voltages never get near the 500 V dc rating of the standard
supply. T herefore, a lower voltage rating capacitor (500 V)
was chosen to fit more capacitance in the same space in order
to better meet the conducted emissions requirement of MIL -
ST D-461D (CE102). For those applications requiring 250 V
or less of isolation from input to output, the present designs
would meet NAVMAT guidelines.
Switching T ransistors:
100 V MOSFET s are used in the
standard unit to switch the primary side of the transformers.
T heir nominal off-state voltage meets the NAVMAT derating
guidelines. When the MOSFET s are turned off, however, mo-
mentary spikes occur that reach 100 V. T he present generation
of MOSFET s are rated for repetitive avalanche, a condition that
was not considered by the NAVMAT deratings. In the worst
case condition, the energy dissipated during avalanche is 1% of
the device’s rated repetitive avalanche energy. T o meet the
NAVMAT derating, 200 V MOSFET s could be used. T he
100 V MOSFET s are used instead for their lower on-state resis-
tance, resulting in higher efficiency for the power supply.
NAVMAT Junction T emperatures:
T he two types of power
deratings (current and temperature) can be independent of one
another. For instance, a switching diode can meet its derating
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