Y402412K7560T9R Datasheet, PDF (2/7 Pages) Vishay Siliconix – Z-1 Foil Ultra High Precision Wrap-around Chip Resistor

FRSM Series of Precision Chip Resistors
Vishay Foil Resistors
ABOUT THE FRSM
Several factors need to be considered when choosing a resistor for
applications that require long term stability, including TCR (ambient
temperature), Power TCR (self heating), load-life stability for more
than 10K hours (instead of the typical 1000 or 2000 hours load-life),
end-of-life tolerance (which is more important than the initial
tolerance), thermal EMF (low values, D.C), thermal stabilization and
ESD. Some precision resistor technologies such as Precision Thin
Film offer designers tight initial tolerances as low as 0.02 % but have
poor load life stability, high end-of-life tolerance, long thermal
stabilization, high drifts during operational life and ESD sensitivity.
Other resistor technologies, such as Wirewounds, provide low
absolute TCR and excellent current noise of -40 dB but have high
inductance and poor rise time (or thermal lag) for more than a few
seconds.
There are essentially only three resistance technologies widely used
for precision resistors in military and space applications: Thin Film,
Wirewound and Bulk Metal® Foil. Each has its own balance of
characteristics and costs that justify its selection in these
applications. Thin Films are most cost-efficient within their normal
range of characteristics but have the highest TCR, highest noise and
have the least stability of the three technologies. Wirewounds have
low noise, low TCR and a high level of stability at moderate cost but
also have high impedance and slow signal response. Wirewounds
can also have a higher power density, but some stability is lost
through temperature cycling and load-life when made in smaller
configurations. Bulk Metal® Foil resistors have the lowest noise,
lowest TCR, highest stability and highest speed of any technology
but may have a higher cost, depending upon model. With Bulk
Metal® Foil resistors, savvy designers often save overall by
concentrating the circuit stability in the foil resistors where
exceptional stability allows for use of less-costly active devices---an
option not available with other resistor technologies because foil
requires a smaller total error budget through all cumulative resistor
life exposures. Also, foil often eliminates extra circuitry added
merely for the purpose of correcting the limitations of other resistor
components. FRSM’s Bulk Metal® Foil resistors, based on new
generation technology and improved production methods starting
from February 2011, offer designers the complete set of top
performance characteristics to simplify circuitry and lower overall
system costs by reducing the number of required parts while
assuring a better end product. The new series of FRSM feature a
long-term load-life stability within 0.0025 % after 2000 hours and
0.005% after 10000 hours under full rated power at + 70 °C, first time
in the history of all resistor technologies. In addition to their low
absolute TCR of almost zero TCR , the devices offer Power TCR
(“ΔR due to self heating”) to ±5 ppm at rated power; tight tolerance
from 0.01% and thermal EMF of 0.05 µV/°C. Current design practice
has been to over specify resistors to allow for expected tolerance
degradation during service and there is a trend to move to
commercial off the shelf (COTS) parts instead of MIL spec Qualified
(QPL) parts. Vishay Precision Group offers a new approach with
lower prices to bring Foil resistors within the reach of designers
whose end-of-life tolerance target is 0.05 % (total end of life
cumulative deviation from nominal) or less with COTS resistors
having all the inherent features for long term reliability.
While other resistor technologies can take several seconds or even
minutes to achieve a steady state thermal stabilization (thermal lag),
Vishay Foil resistors feature an almost instantaneous thermal
stabilization time and a nearly immeasurable 1 ns rise time
effectively with no ringing. The stress levels of each application are
different so the designer must make an estimation of what they might
be and assign a stress factor to each one. The stress may normally
be low but for these purposes, we must assure that the installed
precision resistor is capable of reliability withstanding all potential
stresses. For example, if the resistor is installed in a piece of
equipment that is expected to go out into an oil field in the back of a
pickup truck, shock and vibration and heat from the sun are obvious
factors. The specific causes of resistor drift are listed in Table 4 and
the allowances shown are for full scale exposure. The designer may
choose to use a percentage of full scale stress factor if the
equipment will never see the full scale conditions. For example, a
laboratory instrument that is expected to be permanently installed in
an air-conditioned laboratory does not need an end-of-life allowance
for excessive heat. There are other reasons for tolerancing the
resistors tighter than the initial calculation: Measurement equipment
accuracy is traditionally ten times better than the expected accuracy
of the devices under test. So, these tighter tolerance applications
require a Foil resistor. Also, the drift of the resistor without any
stress factor considerations results in a shift over time that must be
considered. FRSMs have the least amount of time shift. The
manufacturer’s recommended recalibration cycle is a factor in the
saleability of the product and the longer the cycle, the more
acceptable the product. Foil resistors contribute significantly to the
longer calibration cycle.
FIGURE 2 - TRIMMING TO VALUES*
(Conceptual Illustration)
Interloop Capacitance
Reduction in Series
Mutual Inductance
Reduction due
to Change in
Current Direction
Current Path
Before Trimming
Current Path
After Trimming
Trimming Process
Removes this Material
from Shorting Strip Area
Changing Current Path
and Increasing
Resistance
Note: Foil shown in black, etched spaces in white
* To acquire a precision resistance value, the Bulk Metal® Foil chip
is trimmed by selectively removing built-in “shorting bars.” To
increase the resistance in known increments, marked areas are cut,
producing progressively smaller increases in resistance. This
method eliminates “hot spot” and improves the long term stability of
the resistor.
www.vishayfoilresistors.com
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For any questions, contact: [e-mail]
Document Number: 63209
Revision: 7-Apr-11