ADDC02808PBKV Analog Devices, ADDC02808PBKV Datasheet - Page 15

• Manufacturer Part Number: ADDC02808PBKV
• Description: 28 V/ 200 W Pulsed DC/DC Converter with Integral EMI Filter
• Manufacturer: Analog Devices

REV. A
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
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 perfor-
mance of the circuit. Therefore, the standard unit makes the
following exceptions.
Common-Mode EMI Filter Capacitors: The standard sup-
ply 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 V or less of isolation from input to output, the present
designs would meet NAVMAT guidelines.
Switching Transistors: 100 V MOSFETs are used in the
standard unit to switch the primary side of the transformers.
Their nominal off-state voltage meets the NAVMAT derating
guidelines. When the MOSFETs are turned off, however, mo-
mentary spikes occur that reach 100 V. The present generation
of MOSFETs 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. To meet the
NAVMAT derating, 200 V MOSFETs could be used. The
100 V MOSFETs are used instead for their lower on-state resis-
tance, 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 con-
verter, 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 semicon-
ductors. This is covered in the specification table in the section
entitled “Thermal Characteristics”.
EMI CONSIDERATIONS
Figures 11 through 14 show the results of EMI measurements
conducted in accordance with MIL-STD-461D/462D for the
–15–
ADDC02805SA dc/dc converter (28 V
using the test setup shown in Figure 15. The EMI performance
of the ADDC02808PB dc/dc converter will be different for
several reasons. The purpose of this section is to describe the
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.
28 V
ADDC02805SA has an integral differential- and common-
mode EMI filter that is designed to meet all applicable require-
ments in MIL-STD-461D when the power converter is
installed in a typical system setup (described below). The
converter also contains transient protection circuitry that per-
mits 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):
It should be noted that there are several areas of ambiguity with
respect to CE102 measurements that may concern the systems
engineer. One area of ambiguity in this measurement is the
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
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 fre-
quency 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 com-
mon-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 represen-
tative of the final system configuration EMI test. For the fol-
lowing reasons, the same is true if separately packaged EMI
filters are used.
power supply which is conducted externally through its input
power leads)
the power supply which is conducted internally through the
input power leads and may interfere with the supply’s opera-
tion)
power supply which is radiated into the surrounding space)
the power supply which radiates into or through the power
supply and may interfere with its proper operation)
CExxx: conducted emissions (EMI produced internal to the
CSxxx: conducted susceptibility (EMI produced external to
RExxx: radiated emissions (EMI produced internal to the
RSxxx: radiated susceptibility (EMI produced external to
IN
, 100 W Out, Baseline Performance: The
ADDC02808PB
IN
, 5 V
OUT
, 100 W)