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The system/equipment that
contains uprated parts must meet all
safety, mission, and performance requirements. The system/equipment
manufacturer, not the government or the part manufacturer, is responsible for
meeting these requirements.
a. Uprating is a
process to assess the capability of a device to meet the performance
requirements of the application in which the device is used outside the
manufacturer-specified temperature range (term specified by
the Avionics Working Group). For standardization proposes, this term/definition
will be used. Other terms/definitions from the Avionics Working Group are not
yet acceptable for inclusion in this document/database.
b. Derate –
To reduce the voltage, current, or power rating of a part to improve its
reliability or to permit operation at high ambient temperatures.
– The reduction in rating of a part especially the maximum power-dissipation
rating at higher temperatures.
factor – The factor by which the ratings of parts are reduced to provide
additional safety margins in critical applications or when the parts are
subjected to extreme environmental conditions for which their normal ratings do
A part’s operating temperature (TA) range is
the concern when uprating.
Part characteristics. Part manufacturers characterize for
operation over a temperature range (e.g., 0°C to 70°C). Power, voltage and current maximum
ratings are established from this operating temperature. A part that has a
0°C to 70°C operating temperature (TA) range
may have a -65°C to +150°C (TOP) storage temperature range.
In addition, the part’s junction temperature (TJ) will be some other
temperature. Both the operating and storage temperature ranges, on a data sheet,
are established standards and used to warranty the functionality and reliability
of the product. The junction temperature (TJ), which is usually not
listed on a data sheet, is the most critical temperature.
The 0°C to 70°C operating temperature range predates
microcircuits. Microcircuits were invented in the early 1960’s. The
0°C to 70°C operating temperature range was used, as a
standard, as early as the 1950’s and was probably established to control the
failure rates of transistor leakage currents.
Part manufacturers consider the operating
temperature range (0°C to 70°C) as part of their warranty. If a
system/equipment manufacturer uses a part in a higher temperature than the part
manufacturer range the system/equipment takes on the risk and responsibility for
safety, mission, and performance requirements.
System/equipment needs. System/equipment manufacturers, at times,
need to select a part that’s operating temperature range is 0°C to 70°C and their application operating temperature
is greater than 70°C. This is a potential uprating situation. The concern is will
the part function reliable in the application at the higher temperature and
still meet safety, mission, and performance requirements.
To uprate, a
part the system/equipment manufacturer must know the application operating
temperature, functionality and reliability requirements.
Comparing Uprating to Derating. Technically uprating and derating are similar. Below shows
comparison and requirements for part usage.
All parts must meet
safety, mission, and performance requirements including functionality and
No part can exceed its
maximum rated power conditions. That being voltage, current, thermal resistance
and junction temperature.
parameters could be adjusted down or controlled to meet performance temperature
requirements. Examples being slowing the device speed down, heat-sinking the
device, and air or liquid cooling.
The part could be
temperature-sensitivity characterized. This is done to parts that the warranted
operating temperature (TA) range of the part (e.g., 0°C to 70°C) is below the application temperature
(e.g., 80°C). The operating temperature range, of a
part, is not a maximum rated condition. It could be exceeded following a
characterization assessment. Even if the TA is exceeded the part, in
the application, must meet the performance requirements including functionality
and reliability. To meet the application performance requirements including
functionality and reliability the part most likely would have to be derated. Derating is adjusting down a parameter
for the part to meet the application performance requirements. A part that is derated and one that straight out meet
performance requirements, following a characterization assessment, is uprating.