VSH144
Vishay Foil Resistors
Bulk Metal
®
Foil Technology Low Profile Conformally Coated
High Precision Voltage Divider Resistor with TCR Tracking
to 0.5 ppm/°C and Tolerance Match to 0.01 % (100 ppm)
FEATURES
Temperature coefficient of resistance (TCR)
absolute: ± 2 ppm/°C typical
(- 55 °C to + 125 °C, + 25 °C ref.)
tracking: 0.5 ppm/°C
Tolerance: absolute and matching to 0.01 %
(100 ppm)
Power rating: 0.2 W at 70 °C, for the entire resistive
element R
1
and R
2
, divided proportionally between the two
values
Load life ratio stability: < 0.01 % (100 ppm) 0.2 W at 70 °C
for 2000 h
Maximum working voltage: 200 V
Resistance range: 100R to 20K per resistive element
Vishay Foil resistors are not restricted to standard
values/ratios; specific “as requested” values/ratios can be
supplied at no extra cost or delivery (e.g. 1K2345 vs. 1K)
Electrostatic discharge (ESD) up to 25 000 V
Non-inductive, non-capacitive design
Rise time: 1 ns effectively no ringing
Thermal stabilization time < 1 s (nominal value achieved
within 10 ppm of steady state value)
Current noise: 0.010 µV
RMS
/V of applied voltage (< - 40 dB)
Thermal EMF: 0.05 µV/°C typical
Voltage coefficient: < 0.1 ppm/V
Non inductive: < 0.08 µH
Non hot spot design
Terminal finish: lead (Pb)-free or tin/lead alloy
Compliant to RoHS directive 2002/95/EC
Prototype quantities available in just 5 working days
or sooner. For more information, please contact
foil@vishaypg.com
For better performances see VSH144Z (Z-Foil) datasheet
APPLICATIONS
Instrumentation amplifiers
Bridge networks
Differential amplifiers
Military
Space
Medical
Automatic test equipment
Down-hole (high temperature)
R
1
V
in
-
+
R
2
V
out
VSH144
TABLE 1A - MODEL VSH144
SPECIFICATIONS
RESISTANCE
VALUES
500
to 20 k
100
to < 500
ABSOLUTE
TOLERANCE
ABSOLUTE TCR
(- 55 °C to + 125 °C,
+ 25 °C ref.)
TYPICAL AND MAX.
SPREAD
± 2 ppm/°C ± 3 ppm/°C
± 0.01 %
± 0.02 %
TABLE 1B - MODEL VSH144
SPECIFICATIONS
RESISTANCE
RATIO
1:1
> 1:1 to 4:1
> 4:1 to 10:1
>10:1
TOLERANCE
MATCH
0.01 %
0.02 %
TCR TRACKING MAX.
0.5 ppm/°C
1.0 ppm/°C
1.5 ppm/°C
2.0 ppm/°C
FIGURE 1 - TRIMMING TO VALUES
Note
• See table 2 for additional established ratios
Interloop
Capacitance
Reduction
in Series
Mutual
Inductance
Reduction due
to Opposing
Current in
Adjacent Lines
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
* Pb containing terminations are not RoHS compliant, exemptions may apply
Document Number: 63172
Revision: 29-Mar-10
For any questions, contact:
foil@vishaypg.com
www.foilresistors.com
1
VSH144
Vishay Foil Resistors
INTRODUCTION
What is precision?
For resistors, precision is the term used to describe a
combination of attributes starting with accuracy but including
stability with time, temperature and load as well.
There are many causes for a resistor to depart from the
fundamental precept of Ohm's Law and it is in the realm of
precision that this is most demanding and most challenging.
There are ideal solutions to these issues in the form of
Foil-based resistors.
Generally, “precision” resistors are those devices that are
understood to fall within a range of accuracy better than 1 %
and hold their initial value throughout the assembly and life
of the equipment to better than 0.5 %. Resistors that maintain
these characteristics with “orders-of-magnitude better
performance”, such as the foil resistor technology, can be
reasonably termed “ultra-precision”. Of course there are
other considerations such as frequency response that may
govern the selection but starting with these parameters we
can pretty much rule out every technology except Foil, wire,
and deposited metal film in that order of precision.
What is matching?
This term defines to what extent one or more resistors are
referenced to one another as opposed to each resistor
having its own independent specifications, unrelated to other
resistors in the circuit. Usually, one resistor is defined as the
reference resistor and all others are defined relative to the
reference resistor. For example, the reference resistor may
have an absolute (or independent) tolerance of ± 0.1 %, and
other resistors can be specified as “matched” to within
0.01 % of the reference resistor. For a tighter grouping of
three or more resistors, all resistors may be specified as
having a defined match among all the resistors, thereby
keeping the entire grouping of resistors within a tighter
grouping than if they were all refered to just one reference
resistor. The initial “match” refers to the initial supplied
tolerance of each resistor and its relationship to other defined
resistors in the group. However, the initial match is degraded
in application as each resistor in the set responds differently
to board-assembly stresses, temperature excursions,
self-heating from power dissipation, thermal shock, load-life,
etc. So the term “match” may be extended to indicate the limit
of change in the set of resistors as they experience any
number of defined exposures. That is, for example, the set
may be defined as being matched to within 0.01 % initially,
and within 0.05 % after exposure to thermal shock, load-life,
etc. These exposure cause permanent changes in
resistance. Temporary changes are classified in other terms
such as TCR (Temperature Coefficient of Resistance) and
TCR tracking, PCR (Power Coefficient of Resistance), etc
but can be as important or more important than matching in
that they change the relationships among the resistors
immediately while in actual operation.
The differential self heating effect on “matching” is often
overlooked. Even though the initial match is tight and good
TCR “tracking” is exhibited, the same current flow through
the resistors of different values will produce power
dissipation differences (I
2
R self heating) and induce ratio
www.foilresistors.com
2
changes proportional to the absolute TCR.
Therefore the lower the absolute TCR, the less the match will
be affected over temperature changes, including differential
power-induced temperatures.
Additionally, when resistors within a set have different
absolute TCR’s (individual TCR’s - not relative or tracking
TCR), the ratios change even more due to the differential
self-heating as well as to differential ambient temperatures:
ratio
= (TCR track x
temp
1) + (absolute TCR x
temp
2)
where
temp
1 is the change of ambient temperature and
temp
2 is the temperature difference between two resistors
due to differential self-heating.
Differential self-heating can occur, for example, when the
same current flows through resistors of different resistance
values. The construction of the VSH144 keeps both resistors
at the same temperature regardless of resistance value or
differential power.
Since for precision applications the TCR tracking is often
selected to be less than the absolute TCR (e.g.: 15 ppm/°C
absolute selected for 5 ppm/°C track) the absolute TCR is
much more important any time the resistors are at different
temperatures, regardless of the cause. The error in the
match becomes critical when long term ratio stability is
required under small variations of ambient temperature and
self heating, even if selected for excellent initial matching
and tracking.
Bulk Metal Foil resistor dividers have the lowest absolute
TCR and TCR tracking of any technology and therefore have
the best operational and end of life matching for applications
where stability is important.
Why ratio stability is important?
Resistors in divider or network form, are called upon to track
at more than ambient temperature. Throughout the service
life of the equipment, the resistors around the operational
amplifier, for example, are required to hold a defined ratio
even though the dissipation in the feedback resistor is
different from that in the input resistor, causing one to be at
the higher temperature than the other. This is called tracking
under power. If environment stresses cause one resistor to
drift (permanent
R’s)
more than its counterpart, the ratio
changes over a period of time and can be significant. This is
called tracking with time. Foil resistors used in dividers form
share the same substrate for thermal equality and possess a
TCR track of less than 0.1 ppm/°C, they offer the best
combination of temperature-load-time tracking.
The factors that contribute to this are:
1. Fundamentally low absolute TCR
2. Extremely low TCR tracking
2. Very small drift with load over time
3. Common behavior - all parts move the same direction with
temperature, load and time
Our application engineering department is available to
advise and make recommendations. For non-standard
technical requirements and special applications. Please
contact
foil@vishaypg.com.
For any questions, contact:
foil@vishaypg.com
Document Number: 63172
Revision: 29-Mar-10
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