ADDC02808PB(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADDC02808PB Datasheet PDF : 20 Pages
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ADDC02808PB
1400
Once the pulse is over, the converter initiates a soft-start, which
is completed before the next pulse. No degradation of converter
1200
performance occurs.
1000
THERMAL CHARACTERISTICS
800
Junction and Case Temperatures: It is important for the
user to know how hot the hottest semiconductor junctions
600
within the converter get and to understand the relationship
400
between junction, case, and ambient temperatures. The hottest
semiconductors in the 100 W product line of Analog Devices’
200
high density power supplies are the switching MOSFETs and
0
120
125
130
135
140
145
150
the output rectifiers. There is an area inside the main power
transformers that is hotter than these semiconductors, but it is
SHUTDOWN CASE TEMPERATURE – °C
within NAVMAT guidelines and well below the Curie tempera-
OBSOLETE Figure 36. External Resistor Value for Raising
Temperature Shutdown Point
INPUT VOLTAGE RANGE
The steady state operating input voltage range for the converter
is defined as 18 V to 40 V. The abnormal operating input
voltage range is defined as 16 V to 50 V. In accordance with
MIL-STD-704D, the converter can operate up to 50 V dc input
for transient conditions as long as 50 milliseconds, and it can
operate down to 16 V dc input for continuous operation during
emergency conditions. Figure 3 (typical low line dropout vs.
load) shows that the converter can work continuously down to
and below 16 V dc under reduced load conditions.
The ADDC02808PB can be modified to survive, but not work
through, the upper limit input voltages defined in MIL-STD-
704A (aircraft) and MIL-STD-1275A (military vehicles). MIL-
STD-704A defines an 80 V surge that lasts for 1 second before
ture of the ferrite. (The Curie temperature is the point at which
the ferrite begins to lose its magnetic properties.)
Since NAVMAT guidelines require that the maximum junction
temperature be 110°C, the power supply manufacturer must
specify the temperature rise above the case for the hottest semi-
conductors so the user can determine what case temperature
is required to meet NAVMAT guidelines. The thermal charac-
teristics section of the specification table states the hottest junction
temperature for maximum output power at a specified case
temperature. The unit can operate to higher case temperatures
than 90°C, but 90°C is the maximum temperature that permits
NAVMAT guidelines to be met.
Case and Ambient Temperatures: It is the user’s
responsibility to properly heat sink the power supply in order to
maintain the appropriate case temperature and, in turn, the
maximum junction temperature. Maintaining the appropriate
case temperature is a function of the ambient temperature and
it falls below 50 V, while MIL-STD-1275A defines a 100 V
the mechanical heat removal system. The static relationship of
surge that lasts for 200 milliseconds before it falls below 50 V.
these variables is established by the following formula:
In both cases, the ADDC02808PB can be modified to operate
to specification up to the 50 V input voltage limit and to shut
TC = TA + ( P D × RθCA )
down and protect itself during the time the input voltage
where
exceeds 50 V. When the input voltage falls below 50 V as the
surge ends, the converter will automatically initiate a soft start.
TC = case temperature measured at the center of the package
bottom,
In order to survive these higher input voltage surges, the modified
converter will no longer have input transient protection, how-
ever, as described below.
Contact the factory for information on units surviving high
TA = ambient temperature of the air available for cooling,
PD = the power, in watts, dissipated in the power supply,
RθCA = the thermal resistance from the center of the package
to free air, or case to ambient.
input voltage surges.
Input Voltage Transient Protection: The converter has a
transient voltage suppressor connected across its input leads to
protect the unit against high voltage pulses (both positive and
The power dissipated in the power supply, PD, can be calculated
from the efficiency, , given in the data sheets and the actual
output power, PO, in the user’s application by the following
formula:
negative) of short duration. With the power supply connected
in the typical system setup shown in Figure 15, a transient
voltage pulse is created across the converter in the following
manner. A 20 µF capacitor is first charged to 400 V. It is then
connected directly across the converter’s end of the two meter
power lead cable through a 2 Ω on-state resistance MOSFET.
The duration of this connection is 10 µs. The pulse is repeated
every second for 30 minutes. This test is repeated with the
connection of the 20 µF capacitor reversed to create a negative
PD
=
PO
1
η
– 1
For example, at 80 W of output power and 80% efficiency, the
power dissipated in the power supply is 20 W. If under these
conditions, the user wants to maintain NAVMAT deratings
(i.e., a case temperature of approximately 90°C) with an
ambient temperature of 75°C, the required thermal resistance,
case to ambient, can be calculated as
pulse on the supply leads. (If continuous reverse voltage
protection is required, a diode can be added externally in series
at the expense of lower efficiency for the power system.)
The converter responds to this input transient voltage test by
shutting down due to its input overvoltage protection feature.
90 = 75 + (20 × RθCA) or RθCA = 0.75°C/W
This thermal resistance, case to ambient, will determine what
kind of heat sink and whether convection cooling or forced air
cooling is required to meet the constraints of the system.
REV. 0
–13–
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