ADDC02808PB(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADDC02808PB Datasheet PDF : 20 Pages
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ADDC02808PB
Diodes (Switching, General Purpose, Rectifiers)
70% current (surge and continuous) derating
ADDC02805SA dc/dc converter (28 VIN, 5 VOUT, 100 W)
using the test setup shown in Figure 15. The EMI performance
65% peak inverse voltage derating
of the ADDC02808PB dc/dc converter will be different for
110°C maximum junction temperature
several reasons. The purpose of this section is to describe the
Diodes (Zeners)
70% surge current derating
60% continuous current derating
50% power derating
various MIL-STD-461D baseline tests and the
ADDC02805SA converter’s corresponding performance and
then explain how the EMI performance of the ADDC02808PB
will differ from this baseline.
110°C maximum junction temperature
28 VIN, 100 W Out, Baseline Performance: The
Microcircuits (Linears)
ADDC02805SA has an integral differential- and common-
70% continuous current derating
mode EMI filter that is designed to meet all applicable
75% signal voltage derating
requirements in MIL-STD-461D when the power converter is
110°C maximum junction temperature
installed in a typical system setup (described below). The
OBSOLETE The ADDC02808PB 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. Therefore, the standard unit makes
the following exceptions.
Common-Mode EMI Filter Capacitors: The 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. Therefore, 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-
STD-461D (CE102). For those applications which require 250
converter also contains transient protection circuitry that
permits the unit to survive short, high voltage transients across
its input power leads.
Electromagnetic interference (EMI) is governed by MIL-STD-
461D, which establishes design requirements, and MIL-STD-
462D, which defines test methods. EMI requirements are
categorized as follows (xxx designates a three digit number):
• CExxx: conducted emissions (EMI produced internal to the
power supply which is conducted externally through its input
power leads)
• CSxxx: conducted susceptibility (EMI produced external to
the power supply which is conducted internally through the
input power leads and may interfere with the supply’s
operation)
• RExxx: radiated emissions (EMI produced internal to the
power supply which is radiated into the surrounding space)
V or less of isolation from input to output, the present designs
• RSxxx: radiated susceptibility (EMI produced external to
would meet NAVMAT guidelines.
the power supply which radiates into or through the power
Switching Transistors: 100 V MOSFETs are used in the
supply and may interfere with its proper operation)
standard unit to switch the primary side of the transformers.
Their nominal off-state voltage meets the NAVMAT derating
It should be noted that there are several areas of ambiguity with
respect to CE102 measurements that may concern the systems
guidelines. When the MOSFETs are turned off, however,
engineer. One area of ambiguity in this measurement is the
momentary spikes occur that reach 100 V. The present
generation of MOSFETs are rated for repetitive avalanche, a
nature of the load. If it is constant, then the ripple voltage on
the converter’s input leads is due only to the operation of the
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. To meet the NAVMAT derating, 200 V MOSFETs
could be used. The 100 V MOSFETs are used instead for their
lower on-state resistance, resulting in higher efficiency for the
power supply.
NAVMAT Junction Temperatures: The two types of power
deratings (current and temperature) can be independent of one
another. For instance, a switching diode can meet its derating
of 70% of its maximum current, but its junction temperature
can be higher than 110°C if the case temperature of the
converter, which is not controlled by the manufacturer, is
allowed to go higher. Since some users may choose to operate
the power supply at a case temperature higher than 90°C, it then
becomes important to know the temperature rise of the hottest
semiconductors. This is covered in the specification table in the
section entitled “Thermal Characteristics”.
converter. If, on the other hand, the load is changing over
time, this variation causes an additional input current and
voltage ripple to be drawn at the same frequency. If the
frequency is high enough, the converter’s filter will help
attenuate this second source of ripple, but if it is below
approximately 100 kHz, it will not. The system may then not
meet the CE102 requirement, even though the converter is not
the source of the EMI. If this is the case, additional
capacitance may be needed across the load or across the input
to the converter.
Another ambiguity in the CE102 measurement concerns
common-mode voltage. If the load is left unconnected from the
ground plane (even though the case is grounded), the common-
mode ripple voltages will be smaller than if the load is
grounded. The test specifications do not state which procedure
should be used. However, in neither case (load grounded or
floating) will the typical EMI test setup described below be
exactly representative of the final system configuration EMI
test. For the following reasons, the same is true if separately
EMI CONSIDERATIONS
packaged EMI filters are used.
Figures 11 through 14 show the results of EMI measurements
conducted in accordance with MIL-STD-461D/462D for the
REV. 0
–15–
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