CSM Series

Vishay Foil Resistors

www.vishayfoilresistors.com

Document Number: 63089

2

Revision: 3-May-11

ABOUT CSM

(Low Ohm Value 1 m

Ω to 200 mΩ)

Ω to 200 mΩ that features an improved

load-life stability of ± 0.2 % at + 70 °C for 2000 h at rated

power, an absolute TCR of ± 15 ppm/°C maximum from

- 55 °C to + 125 °C, + 25 °C ref., and a tolerance of ± 0.1 %.

Typical current sensing resistors offer a load-life stability of

≥ 1 % through a 2000 h workload. The improved resistance

stability of the CSM

Series makes it ideal for

tightened-stability voltage division and precision current

sensing applications in switching linear power supplies,

power amplifiers, measurement instrumentation, bridge

networks, and medical and test equipment. In addition, the

CSM Series complies with EEE-INST-002 (MIL-PRF 55342

and MIL-PRF 49465) for military and space applications.

Traditional Passive current sensors and shunts generate

heat under power, which changes their resistance, and thus

their voltage output. The CSM’s low absolute TCR reduces

errors due to temperature gradients, thus reducing a major

source of uncertainty in current measurement. The CSM

can withstand unconventional environmental conditions,

including the extremely high temperatures and radiation-rich

environments of down-hole oil exploration and well logging,

or the deep-sea underwater repeaters in cross-ocean

communications.

The stability of the CSM can be further enhanced by

post-manufacturing operations (PMO), such as temperature

cycling, short-time overload, and accelerated load life which

The device features a low thermal electromotive force (EMF)

that is critical in many precision applications. The CSM’s

resistive element with welded copper terminations, plated for

soldering. The terminations make true ohmic contact with the

resistive layer along the entire side of the resistive element,

thereby minimizing temperature variations. Also, the resistor

element is designed to uniformly dissipate power without

creating hot spots, and the welded terminations material is

compatible with the element material.

These design factors result in a very low thermal-EMF

(3 µV/°C) resistor, because in addition to the low thermal

EMF compatibility of the metals, the uniformity and thermal

efficiency of the design minimizes the temperature

differential across the resistor, thereby assuring low thermal

EMF generation at the leads. This further reduces the

“battery effect” exhibited by most current-sensing or

voltage-reference resistors. Thus, the parasitic voltage

generated at the junction of two dissimilar metals, which is

especially important in low-value current-sensing resistors, is

minimized, while the pure current-to-voltage conversion is

protected from such interference in DC applications.

The stability problems associated with analog circuits are

very pervasive, but knowledgeable selection of a few

high-quality resistors, networks, or trimming potentiometers

in critical locations can greatly improve circuit performance,

long-term application-related performance, as well as the

designer’s peace-of-mind.

Additionally, the overall system cost is often reduced when a

knowledgeable designer concentrates costs in a few

exceptionally stable components whose proven minimal-

deviation load and environmental stability can often eliminate

the necessity of additional compensating circuitry or

temperature-controlling systems. The higher reliability and

better overall system performances also achieve excellent

product results in the field, enhancing market acceptance

and product reputation.

Designers often unnecessarily pay for tighter tolerances than

required simply to accommodate the resistance stability

shifts they know to be imminent in an application due to the

large application-related changes in the components they

selected. Selection of a high-stability component like the

CSM in these applications eliminates the need for shift

allowance due to “planned instability” and allows the use of

looser initial tolerances than would be necessary with

current-sensing resistors based on other technologies.

The Key Applications

Applications requiring accuracy and repeatability under

stress conditions such as the following:

• Switching and linear power supplies

• Precision current-sensing

• Power management systems

• Feedback circuits

• Power amplifiers

• Measurement instrumentation

• Precision instrumentation amplifiers

• Medical and automatic test equipment

• Satellites and aerospace systems

• Commercial and Military avionics

• Test and measurement equipment

• Electronic scales