ADDC02812DATV Просмотр технического описания (PDF) - Analog Devices
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ADDC02812DATV Datasheet PDF : 20 Pages
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ADDC02812DA/ADDC02815DA
NAVMAT DERATING
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. The 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 temperature of the
semiconductor devices in a power supply. The NAVMAT
component deratings applicable to the ADDC02812DA and
ADDC02815DA are as follows:
Resistors
80% voltage derating
50% power derating
Capacitors
50% voltage and ripple voltage derating
70% ripple current derating
Transformers 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
Transistors
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
The ADDC02812DA and ADDC02815DA, with one excep-
tion, 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 stan-
dard 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,
momentary spikes occur that reach 100 V. The present genera-
tion 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.
Output Rectifiers (ADDC02815DA only): Schottky diodes
are used as output rectifiers for the ± 15 V dc converter. The
reverse voltage stress on these diodes under normal operating
conditions is 75% of their maximum rating, compared to a
NAVMAT derating guideline of 65%.
REV. A
–13–
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