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CURRENT SENSING RESISTORS solutions guide

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Current Sensing Resistors solutions guide

2 C u r r e n t S e n s i n g R e s i s t o r s 3D i a l 1 - 8 0 0 - C A L L - T T I f o r S o l u t i o n s

About TTI, Inc.

Why Acquire Current Sensing Resistors From TTI?TTI is the world’s largest distributor of current sensing components. TTI maintains an extensive inventory and offers the best current sensing choices in the industry, meeting almost any requirements of customers. The company’s basic strategy is to focus on a specific range of products and strive to be the industry’s leading distributor. No other company offers the unique combination of benefits that TTI provides.

Product Knowledgeable ExpertsThe team of specialists at TTI has more experience in the current sensing product areas than any other distributor. All TTI employees participate in company-wide training programs, which have helped create the most product-knowledgeable team in the industry. Additionally, customers dealing with the complexities of current sensing components can rely upon the TTI sales team as a valuable resource of information and guidance.

The 80/20 RuleThe parts sold by TTI comprise 80-85 percent of the components used in electronic equipment. But, because the components are so inexpensive, they represent only about 5-10 percent of the total cost. When customers rely onTTI to supply passive, interconnect, and electromechanical components, they resolve 80 percent of their potential problems, freeing them to focus on semiconductors, subassemblies, and PCBs, which offer a better return on theirefforts.

Broader And Deeper InventoriesTTI maintains extensive inventories, stocking more than 200,000 parts, with more than 80 percent available for immediate delivery. That’s more passive and interconnect parts than from any other source. TTI’s product department ensures that the parts stocked are the right parts needed by customers today.

Close Supplier RelationshipsTTI partners with only the leading components manufacturers in the world, structuring a solid supply base to establish a partnership with each manufacturer. As a group, these companies allow TTI to provide the best approved vendor list (AVL) coverage imaginable. These suppliers are industry leaders in new component technologies. This means TTI is able to enlist the help of a manufacturer to solve any potential design problems that may arise for customers.

Quality And ReliabilityTTI’s 30-year commitment to quality and service excellence means reliability for the customer. Whenever possible, TTI takes advantage of technology to shorten process times and reduce likelihood of errors. TTI implementedTotal Quality Management in 1989 to further solidify a commitment to quality, and has been registered to the most current ISO 9000 standard since 1993. Today, TTI has one global documentation system, allowing every branch andwarehouse operated by TTI throughout the world to employ the same processes. Year after year, customers rate our quality and management practices to be among the very best in the industry. Contact your local sales branch to learn more about TTI quality systems and results.

Services And Special ProgramsTTI is experienced, committed and well prepared to meet your current sensing component needs. From component labeling to in-plant stores, TTI helps customers find, buy, receive, and use components in the most cost-efficient way. For more information on parts modification, electronic information exchange, and supply chain management programs contact a TTI branch location today. ❖


About TTI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

An Introduction to Current Sensing Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Engineering Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Current Sensing Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

TT Electronics / IRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

KOA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Vishay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Panasonic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

While every effort has been made to ensure that the information contained within is accurate and up to date, TTI, Inc. makes no warranty, representation or undertaking whether expressed or implied, nor does it assume any legal liability, whether direct or indirect, or responsibility for the accuracy, completeness, omissions, or usefulness of any information.

Copyright © 2003 TTI, Inc.

Table of Contents


An Introduction to Current Sensing ResistorsWhat Is A Current Sensing Resistor?Current sensing products are the newest and fastest growing resistive products in the industry today. As with most passive products, the majority of new designs are surface-mount. These resistors are used to monitor the current in a circuit and translate the amount of current in that circuit into a voltage that can be easily measured and monitored.

How Do They Work?As stated by Ohm’s Law, there is a voltage drop across any resistance when current is fl owing. A current sensing resistor is designed for low resistance so as to minimize power consumption. As a result, the calibrated resistance senses the current fl owing through it in the form of a voltage drop which is detected and monitored by the control circuitry. In summary, current sensing resistors translate current into a voltage which is monitored by the controlled circuitry.

What Does The Future Hold?As the world becomes more and more technology-driven, the uses for current sensing resistors will continue to increase. The need for even lower resistance value ranges is already becoming evident, as is the need for these resistors to handle more power. The trend industry-wide is smaller and smaller products, so look for many new products to emerge over the next few months that will fi ll these requirements. Call TTI for up-to-date information on the latest current sensing products.

Current OptionsTTI carries a wide variety of current sensing products from the industry’s leading manufacturers, such as Vishay, IRC, KOA and Panasonic. This enables us to offer you an astounding number of possible solutions for your circuit design needs. We have everything from a .1 ohm in an 0402 package to the larger fi ve watt open-air sensor available in a low .004 ohm. As you look through the following pages at our vendor- specifi c products, we are confi dent you will fi nd the products you need.

Where Can They Be Used?There are a multitude of uses for this product. Here are some applications already using current sensing products:

• General Use: power supplies, disk drives, battery power management, control of current detection or over-current detection, motor start, high voltage and precision applications.

• Consumer Goods: power tools, thermostats, appliances, televisions, smoke detectors, and video cassette recorders.

• Automotive: anti-lock brake systems, keyless entry systems, air bags, power steering, control systems, voltage regulators, power train, information centers as well as engine controls and modules.

• Telecom: telephones, cell phones, pagers, mobile radios, hand-held devices and laptops.

• Medical & Instrumentation: monitoring systems, pressure sensors, implant products, electronic scales and a variety of diagnostic equipment.

• Military & Aerospace: satellites, missiles, surveillance equipment, sonar and avionic products. ☛


The following are just a few examples to demonstrate when or why a current sensing resistor could be used.• An engineer would want to monitor current in several applications, such as in a power supply, making sure it

is not damaged by receiving too much current. • Current sensing resistors would be used to sense whether or not electricity is fl owing in a circuit; for example

to check whether a light bulb is burned out on an instrument panel. • Some are used to sense how much current is being applied to a battery pack during charging in order to

prevent overcharging or overheating in the batteries. • They can also be used to measure the amount of current being applied to a circuit from the battery pack,

enabling estimation of the battery life before charging is needed. • Another possible application would include being used in a circuit to estimate the rotational speed of a motor,

since the speed of a motor is directly proportional to the amount of current applied to it.

Current Detecting ResistorsThe fi gure below shows the current detecting circuit of a DC/DC converter. The voltage across the current detecting resistor is fed back to control the output power. The resistance should be low to reduce the power dissipation, and the resistor should stand against repeated rush current. Furthermore, the self-inductance should be for high frequency applications. Recommended types are general purpose current sensing products or a fl ame retardant type.

DC/DC converter utilizes current sensing resistors with Ultra Low 14 Low TCR, tight tolerance, high current capability, and low thermal EMF.

Due to the increase in sales of notebook PCs, the demand for the DC/DC converter has shown rapid growth because of its high-energy conversion effi ciency (95 percent vs. 50 to 10 precent for the Conventional IC Regulator), and its precise current-limiting capability.

However, to assure the performance of the multiple output DC/DC converter, the current limiting voltage must be detected precisely to protect an expensive notebook PC from an overload, which is generally due to shorts within the capacitors used in these devices.

For high-energy conversion effi ciency various control ICs have been developed that utilize resistive components. To achieve the perfect cutoff mode of the DC load current at the programmed current-limiting voltage of the control IC, a very stable and accurate sense resistor with the following characteristics is required for precise voltage comparison:

• Very Low Ohmic ValueFor maximizing energy conversion effi ciency of the DC/ DC converter, the ohmic value for minimizing power consumption at the current sensing resistor, should be below 25 milliohms. ☛


• Tight ToleranceFor maximizing the current supply within the limit of acceptable current, the tolerance of the sense resistor must be ± 1 percent or tighter.

• Low TCRSince the maximum normal DC load current is in excess of three amps, in general, the maximum ΔR due to self-heating must be as low as 1000ppm across the ambient temperature range of 0°C to + 60°C. Thus, a low TCR is required for current sensing.

• Low Thermal EMFFor an accurate comparison between the programmed current-limiting voltage (typically, ≤100mV) of the control IC and the detected voltage by the sense resistor, the error due to thermal EMF of the sense resistor must be minimized. Current level is programmed by the user by choosing ohmic value of the current sensing resistor.

• Resistance ValueFor maximizing energy conversion effi ciency of the DC/DC converter, the value of the current sensing resistor is calculated according to the worst-case low current- limiting threshold voltage of the control IC and the peak inductor current by the following equation:

VLRs = I peak

Where: Rs= Sense Resistor (Ω)I peak = Peak Inductor Current = (Maximum DC Load Current) x 1.15VL = Worst-case-low current-limiting threshold voltage

The key factor in determining the resolution (current limiting threshold voltage) of the control IC is its semiconductor noise. Typical resistance values utilized in various control ICs are 20 to 25 milliohms.

Terminal ConstructionAs low as one milliohms, two-terminal construction is accepted for the DC/DC converter. However, when better accuracy is required, four-terminal resistors are available. Four- terminal construction will reduce as mounted resistance tolerance variations:

• reduce lead resistance• reduce TCR of copper terminal• reduce TCR of solder joint

High Current CapabilityThe maximum DC load current of an up-to-date notebook PC with high-speed CPU, large memory (DRAM) and the CD-ROM is in excess of three amps. In this case, the sense resistor must be able to withstand a high continuous current of at least 1.15 times the DC load current (peak inductor current) due to the effect of the inductor connected in series for smoothing the circuit. Otherwise, the DC/DC converter will fail to function due to a failed sense resistor. ☛


High Temperature CapabilityUtilization of DC/DC converters in industrial and automotive applications may expose components to higher temperature environments. The sense resistor must be capable of operating in high temperature conditions with minimal reduction (derating) of rated power.

TCRAt steady state conditions, notebook PCs generally require input currents in excess of three amps. For accurate current limiting control by the control IC, the DR of the sense resistor, due to self-heating, must be low enough to ensure that the accuracy of comparison between the worst-case-low current-limiting threshold voltage of the control IC and the sense resistor voltage is ± 5 percent.

To meet this standard current limit, the dynamic tolerance (no load, static resistance tolerance plus percentage of ΔR caused by self-heating plus apparent percentage of AR caused by thermal EMF) allocated to the sense resistor is two percent. To assure two percent tolerance of the sense resistor across the temperature range of 0°C to +100°C (ambient temperature plus self-heating), the resistor must have a low TCR.

Typical Control IC for Dual Output Step-down DC/DC ConverterThe two key functions of a control IC are to supply dual step- down DC potential energy and to perform accurate current limiting which is programmed by the user.

A voltage drop across a sense resistor connected in series between the N-channel power MOSFET and the output terminal is monitored in order to compare the worst-case low current-limiting threshold voltage of the Control IC with the current level programmed by the user via sense resistor.

The sense resistor also functions as apart of the smoothing circuit to supply high linear DC current.

The sequence of the dual output step-down converter’s steady state operations is as follows: fi rst the gate (Ga) turns on the N- channel Power MOSFET (A) and sinks the DC current into the load until the terminal voltage reaches the programmed positive voltage of the control IC. Secondly, (Ga) cuts off (A), and (Gb) turns on (B), and leaks the DC current to the load until the terminal voltage reaches the programmed negative voltage, then, third (Gb) cuts off (B).

Intelligent Li-ion Rechargeable BatteryIntelligent Li-Ion rechargeable batteries utilize current sensing resistors with ultralow ohm, low TCR, tight tolerance, high withstanding surge current and low thermal EMF. In the fi eld of portable electronic equipment such as notebook PCs, mobile telephones and camcorders, the demand for intelligent Li-ion rechargeable batteries has shown rapid growth because their high energy density (approximately 1.5 times in volume and two times by weight compared to Ni-MH batteries), high output voltage (.3 V to 4 V), and low soft discharge rate (10 percent to 12 perecent). ☛


However, to assure the performance of intelligent Li-ion rechargeable batteries, three inherent diffi culties must be taken into account. First, heavy current discharge will cause degraded performance, i.e., available energy will drop down to 90 percent, and sometimes 50 percent of nominal energy. Second, high internal impedance causes a potential drop, which makes it diffi cult to utilize the expected potential energy at high effi ciency. Third, required constant-current and constant-voltage charging is diffi cult to control.

To solve these diffi culties, various intelligent electronic charger and monitoring circuits utilizing resistive components have been developed.

Sense Resistor-General ApplicationFor the precise determination of charge and discharge activities of the battery, very stable and accurate sense resistors with the following characteristics are required:

• Very Low Ohmic ValueFor minimizing energy loss, the required ohmic value is below 100 milliohms.

• Tight ToleranceTo maintain the total accuracy of the intelligent Li-ion rechargeable batteries as close as + 5 percent, – 0.6 percent of the total available power capacity, the tolerance of the sense resistor must be ± 1 percent or tighter.

• Low TCRSince the maximum normal operating current is generally three to four amps, the maximum ΔR due to self-heating must be as low as 1000ppm across the ambient temperature range of 0 to +40°C. Thus, a low TCR resistor for current sensing is required. See Figure 1 for comparison.

• Low Thermal EMFIn standby mode, a notebook PC requires 50 to 10 milliamps to operate its DRAM and CPU, and a Handycam® requires fi ve milliamps to operate its small memory. Therefore, in the standby mode, the thermal EMF of the sense resistor must be low compared to the terminal voltage generated by the current output.

• Resistance ValueFor minimizing the power loss and charging time, and maximizing the effi ciency of the potential energy of the intelligent Li-ion rechargeable batteries to the connected equipment, the sense resistor must be as close to zero as possible. However, this ideal condition is unrealizable since the limited resolution of a microcomputer requires a certain level of voltage between the terminals of the sense resistor.

The key factors to determine the resolution of the microcomputer are its semiconductor noise and offset voltage. Typical resistance values utilized in various microcomputers are 100, 50, 20 and 10 milliohms. ☛

Fig. 1: High Ohmic Values Increase The Time For Charging And Causes Large Power Loss


In comparison, with conventional cermet chips, four to six chips are needed to achieve very low ohmic values. Even with conventional thin film chips, at least two chips are needed do to their low power capability. With a low ohmic, higher power current sensing resistor only one component need be used.

Microcomputers for Intelligent Li-ion Rechargeable batteriesMicrocomputers have various functions to maintain an accurate record of the available capacity of intelligent Li-ion rechargeable batteries:

• Monitor a voltage drop across a sense resistor, connected in a series between the negative battery terminal and ground, and to determine the charge and discharge activity of the battery.

• Apply accurate compensations for battery temperature and rate of charge or discharge and self-discharge calculations to provide available capacity information across a wide range of operating conditions.

• To automatically recalibrate the battery capacity or to learn the capacity in the course of a discharge cycle from full to empty.

The sequence of battery charging is, first, constant current charging until the terminal voltage reaches 4.1 V or 4.2V. Then second, switched to constant voltage charging mode until full charge is achieved. Immediately after full charge is achieved, the sequence must be stopped.

Intelligent Charger Circuits

There are two basic Intelligent Charger Circuits:

Active Potential—Conventional TypeWhen the intelligent Li-ion rechargeable batteries are removed from the equipment, the potential between the terminals is still active (see Figure 2). In the case of short-circuit by misuse, they could be seriously damaged due to an abnormally high discharge current. Therefore, intelligent Li-ion rechargeable batteries require protective resistors or fuse resistors to cut off the abnormally high current. This inactivates the circuit.

When removed from the equipment, the potential between the terminals is still active. Thus, to protect the charging circuit, fuse resistors which burn out at high currents are used.

Non-Active Potential—Advanced Type

When the Intelligent Li-ion rechargeable batteries are removed from the equipment, the potential between the terminals is zero. (see Figure 3). Thus, they do not have a chance of electrical short circuit.

Resistors with reduced self-inductance improves sensing accuracy. ☛

Fig. 3: Non-Active Potential (Advanced Type)

Fig. 2: Active Potential Type (Conventional Type)


A typical application of resistors of extremely low resistance is to detect the current in a switching regulator circuit. But if a parasitic inductance exists, then it may cause an error in the measurement. Assuming that di/dt=30A/us, R=1M~, then self-inductance of the resistor = 1nH. (A typical through-hole has an estimated 0.5nH of inductance). Then a spike voltage as large as 30mV is corresponded to 30A. Resistors are produced to minimize the self-inductance. Reduced inductance resistors are a good choice for high frequency applications.

Resistors to detect the over-currentAs a means to detect the current passing through the transistor, a resistor series is added between and emitter and a ground. This resistor should neither emit smoke nor catch fi re even when the switching transistor breaks down to be subjected to a larger current. In addition, reduced parasitic inductance is required, particularly for the high frequency switching control. Resistors offering very low resistance are required in this scenario. (See Figure 4).

Practical Method to Measure The Electric Current—The Four Point Probe MethodIt is convenient to add a resistor to the network to measure the electric current. Measuring the voltage across the resistor indicates the current that fl ows through it. The resistance should be low enough not to disturb the circuit condition and dissipate the spurious power. But when the resistance is very low, the resistance of the printed circuit pattern may cause error to the measurement. A precision resistor is not applicable in that case. A practical circuit pattering solution is known as Kelvin’s four-terminal method, where the terminals to supply current and the terminals to detect voltage are prepared as illustrated (see Figure 5). Then the detected voltage is exactly proportional to the current, regardless of the resistance of the current supply printed pattern. Input resistance of the voltmeter (not shown) is assumed larger than the current detecting resistor. There are special purpose resistors built in four-terminal for precise electric current measurement. ❖

Fig. 5: Four Point Probe Method

Fig. 4: Current Detecting Cirucit of a DC/DC Converter


Vishay Kits

WSL/WSR Series Kit

15 pcs/ value

WSL-1206 1% WSL-1206 1% WSL-1206 1% WSL-2010 1% WSL-2010 1%

.006, .01, 015 .02, .025, .05 .1, .2 .25 .006, .01, .015 .02, .025, .05

WSL-2010 1% WSL-2512 1% WSL-2512 1% WSL-2512 1% WSL-2512 1%

.1, .2, .25 .005, .01, .012 .015, .018, .02 .025, .03, .04 .05, .07, .075

WSL-2512 1% WSL-2512 1% WSR-2 1% WSR-2 1% WSR-2 1%

.1, .15, .2 .25, .4, .5 .005, .008, 01 .02, .025, .05 .1, .2, 1

IRC Kits

LR/LRF Series Kit

20 pcs/ value

LRF1206, .01, (1%) LRF1206, .015, (1%) LRF1206, .02, (1%) LR1206, .05, (1%) LR1206, .1, (1%)

LRF2512 , .003, (5%) LRF2512 , .005, (5%) LRF2512 , .01, (1%) LRF2512 , .02, (1%) LRF2512 , .025, (1%)

LRF3W, .003, (5%) LRF3W, .004, (5%) LRF3W, .015, (1%) LRF3W, .025, (1%) LRF3W, .05, (1%)

KOA Kits

TLR2B Series Kit

20 pcs/ value 2L, 3L, 4L, 5L, 6L, 8L, 10L, 11L, 12L, 13L, 14L, 15L, 16L, 18L, 20L (1%)

UR73 Series Kit

20 pcs/value 47L, 51L, 56L, 62L, 68L, 75L, 82L, 91L, R10 (1%)

SL1L-F Series Kit

20 pcs/ value

5L00, 5L10, 5L62, 6L04, 6L19, 7L50, 8L00, 8L25, 9L09, 10L0, 11L0, 12L0, 5L00, 5L10, 5L62, 6L04,


R100, R110, R121, R130, R150, R162, R221, R237, R243, R267, R301, R332, R357, R392, R432, R475

R510, R562, R619, R680, R750, R825, R909, 1R00, 475R

SL2L-F Series Kit

20 pcs/ value


6L19,7L50, 8L25, 9L09, 10L0, 11L0, 12L1, 13L0, 43L2, 47L5, 51L0, 56L2, 61L9, 75L0, 82L5, 90L9,

R100, R110, R121, R130, R150, R162, R221, R237, R243, R267, R301, R332, R357

SR73 Series Kit

50 pcs/ value Kits are available in each size (0402-2512). Call for specific values in each kit.

Panasonic Kits

ERJ-L/ERJ-M Series Kit

10 pcs/ value

ERJ-M1WTJ1M0U ERJ-M1WTJ1M5U ERJ-M1WTJ2M0U ERJ-M1WSF3M0U ERJ-M1WSF4M0U

2512, 1 W, .001, 5% 2512, 1 W, .0015, 5% 2512, 1 W, .002, 5% 2512, 1 W, .003, 1% 2512, 1 W, .004, 1%

ERJ-M1WSF5M0U ERJ-M1SF10MU ERJ-M1WSF15MU ERJ-M1WSF20MU

2512, 1 W, .005, 1% 2512, 1 W, .01, 1% 2512, 1 W, .015, 1% 2512, 1 W, .02, 1%

50 pcs/ valueERJ-L1WKF10CU ERJ-L12KF50MU ERJ-L12KF10CU ERJ-L14KF33MU ERJ-L14KF50MU

2512, 1W, .1, 1% 1812, .5 W, .05, 1% 1812, .5 W, .1, 1% 1210, .5 W, .033, 1% 1210, .25 W, .05, 1%

Engineering Kits AvailableTo order engineering kits or to learn more regarding the specific values included in an individual kit, please contact your TTI account representative or call 1-800-CALL-TTI.


Surface Mount Current Sensing Series Packaging Information

Mfg. Series Watts Range Tolerance (%) Bulk Min. Reel Full Reel

WSL0805 / -18 0.125 / .25 .01 - .2 .5, 1 100 1000 (TR) 5000 (RT1)

WSL1206 / -18 0.25 / .50 .002 - .2 .5, 1 100 1000 (TR) 4000 (R86)

WSL2010 / -18 0.50 / 1.0 .001 - .5 .5, 1 100 1000 (TR) 4000 (R86)

WSL2512 / -18 1.0 / 2.0 .001 - .5 / .01 .5, 1 100 1000 (TR) 2000 (R86)

WSL1506E 0.25 .5-10k .5, 1 100 1000 (TR) 4000 (R86)

WSL2010E 0.5 .5-10k .5, 1 100 1000 (TR) 4000 (R86)

WSL2512E 1 .5-10K .5, 1 100 1000 (TR) 2000 (R86)

WSR-2 2 .001 - 1 .5, 1, 5 100 1000 (TR) 1500 (R86)

WSR-3 3 .001 - .2 .5, 1, 5 100 1000 (TR) 1500 (R86)

WSC-1/2 0.5 .1 - 4.99 .5, 1, 5 100 1000 (TR) 2000 (R86)

WSC-1 1 .1 - 2.77K .5, 1, 5 100 1000 (TR) 2000 (R86)

WSC-2 2 .1 - 4.92K .5, 1, 5 100 1000 (TR) 1200 (R86

WSC2515 1 .1 - 2.77K .5, 1, 5 100 1000 (TR) 2000 (R86)

WSC4527 2 .1 - 4.92K .5, 1, 5 100 1000 (TR) 1200 (R86)

WSC6927 3 .1 - 8K .5, 1, 5 100 1000 (TR) 1450 (R86)

WSF2012 0.5 5 - 1.43K .5, 1, 5 100 1000 (TR) 2000 (R86)

WSF2515 1 26.5 - 10K .5, 1, 5 100 1000 (TR) 2000 (R86)

WSF4527 2 10 - 100K .5, 1, 5 100 1000 (TR) 1200 (R86)

WSL3637 3 0.003 - 0.01 .5, 1, 5 100 1000 (TR) 4000 (R86)

WSK2512 1 .001 - .025 .5, 1 100 1000 (TR) 2000 (R86)

WSZ6720 1.8 1 - 3.3K 1, 2, 5, 10 100 n/a 1250 (R86)

WSZ7532 3.75 1 - 15K 1,3, 5, 10 100 n/a 350 (R86)

LR(F)1206 0.5 .005 - 1 1, 2, 5 100 1000 (TR) 4000 (4K)

LR(F)2010 1 .003 - 1 1, 2, 5 100 1000 (TR) 4000 (4K)

LR(F)2512 2 .003 - 1 1, 2, 5 100 1000 (TR) 2000 (2K

LRF3W 3 .003-.1 1, 2, 5 n/a n/a 1800 (TR)

SC3 3 1 - 350 1, 2, 5 n/a n/a 1000

D2PAK (TO263) 25W .2 - 1K 1 100 n/a n/a

WSML1 1 .005 - 10K 1, 5 n/a 1000 (TR) n/a

WSML2 2 .005 - 10K 1, 5 n/a 1000 (TR) n/a

OARS 1 .003 - .05 1, 2, 5 100 n/a 1900

CSS 1 .0005 - .002 1, 3, 5 n/a n/a 1900

PWC0805 0.125 1 - 10M .5, 1, 5 n/a n/a 3000

PWC1206 0.33 1 - 10M .5, 1, 5 n/a n/a 3000

PWC2010 0.75 1 - 10M .5, 1, 5 n/a n/a 3000

PWC2512 1.5 1 - 10M .5, 1, 5 n/a n/a 2000

CSC/CSL 5 .001 - .005 1, 5 1000 n/a n/a

OLV 1,3,5 .003 - .03 5, 10 1000 n/a 2000

WSM1 1 .01 - 1K 1, 5 n/a n/a 1500 (TR)

WSM2 2 .01 - 2K 1, 5 n/a n/a 800 (TR)

WSM3 3 .01 - 10K 1, 5 n/a n/a 750 (TR)

Current Sensing Series


Surface Mount Series (cont.) Packaging Information

Mfg. Series Watts Range Tolerance (%) Bulk Min Reel Full Reel

SR73 0402 - 2512 .024 - 10 1, 2, 5 n/a n/a 5000

SL1 1 .005 - 1M 1, 5 n/a n/a 1000

SL2 2 .005 - 1M 1, 5 n/a n/a 1000

NPR1 1 .01 - 22M 1, 5 n/a n/a 1000

NPR2 2 .01 - 22M 1, 5 n/a n/a 1000

TLR3A 1 .001 - .004 1, 5 n/a 1000 2000

TLR2B 0.5 .002 - .02 1 n/a n/a 5000

UR732A 0.125 .033 - .1 1, 5 n/a n/a 5000

UR732B 0.25 .002 - .02 1, 5 n/a n/a 5000

LR72 .25, .50, 1 .002 - .008 5 1000 n/a 1500

CSR 1, 2 .005 - .05 .5, 1 n/a n/a 1000

ERJ-M1W 1 .002 - .02 1, 5 n/a n/a 3000

ERJ-xR 0603 - 1210 .1 - 9.1 1, 2, 5 n/a n/a 3000

ERJ-L0x 0603 - 1206 .047 - .1 5 n/a n/a 3000

ERJ-Lxx 1210 - 2412 .002 - .1 1, 5 n/a n/a 3000

Leaded Current Sensing Series Packaging Information

Mfg. Series Watts Range Tolerance (%) Bulk Min Reel Full Reel

SR5 5 .004-.05 1, 5 500 n/a n/a

SPU 1, 2, 4, 5 .001- .5 .1, .25, .5, 1, 3, 5 25 n/a n/a

CPL 3, 5, 7, 10, 15 .01-.1 1, 2, 3, 5, 10 100 n/a n/a

CPSL 3, 5, 7, 10, 15 .01-.1 3, 5,10 100 n/a n/a

SPR 1, 3, 5 .0005- .25 .5, 1, 1.5 25 n/a n/a

LVR 1, 3, 5,10 .005- .8 1, 3, 5, 10 100 n/a 1000

OAR 1, 2, 3 .005- .10 1, 5 500 n/a n/a

TFP TO220 20 .01- 1K 1, 5, 10 100 n/a n/a

LOB 1, 3, 5 .005 -.1 1, 5 1000 n/a 1000

PLO 3, 5, 7, 10, 15 .005- .18 1, 2, 3, 5, 10 500 n/a n/a

4LPW 3, 5, 7, 10, 15 .005-1.0 1, 2, 3, 5, 10 100 n/a n/a

PWRL 3, 5, 7, 10 .01-.18 1, 2, 3, 5, 10 500 n/a n/a

CSL 5 .00025-.0025 1 100 n/a n/a


Performance and ReliabilityTT electronics has expanded its line of thick fi lm current sensing resistors to offer a wider range of power ratings from .5 to 25 watts. Offering more design fl exibility, the current sensing line includes surface-mount chips (including the industry’s smallest three watt chip resistor) and high-power metal tab resistors in standard industry packages. When cost-effective performance and reliability are paramount, always specify TT Electronics.

LR Series – Surface-MountThe LR’ family of resistors utilizes IRC’s patented low resistance thick fi lm materials which offer the capability of achieving resistances down to .003 ohms with a low temperature coeffi cient of resistance. The materials are processed on an alumina ceramic substrate, which creates superior thermal conductivity over other substrate technologies. High thermal conductivity results in signifi cantly lower operating temperature and the potential for higher power dissipation. Additionally, the planar resistance path creates advanced high frequency characteristics. LR series components display excellent power handling capability, and the LRF3W series offers three watt power dissipations using a one watt size footprint.

LR Series—An Indepth Look At Its DevelopmentThe LRC series was developed originally to produce resistance values greater than .025 ohms. At the time of its development, it was not foreseen that lower resistance values would be needed. However, as current sensing requirements below .025 ohms became necessary, it was discovered that when the resistor element was on the top surface, variations in the customer’s manufacturing process (solder amount, etc.) coupled with slight variations in the resistance created by the wrap-around end terminations, made insuring the parts’ tolerance when installed on the board diffi cult. As a result, the LRF confi guration with the resistor element on the bottom side was developed, which resolved the situation.

The SC3 and LRF-3W are both rated at three watts in what is typically a one watt package size. The component can dissipate this much power due to IRC’s use of printed thick fi lm cooper as end termination, a factor that separates IRC from the majority of other resistor manufacturers. This material is inexpensive and can be printed relatively thick to act as a “heat pipe” to remove heat from the chip and to equalize the temperature distribution across the chip and effectively radiate the heat into the air.

The resistance vs. frequency characteristics of the LR series is very linear, with a very fl at impedance curve that is nearly pure resistance.

Measurements beyond two GHZ show that the inductance of the chip is approximately 0.2nH regardless of resistance value or size confi guration. These superior characteristics are primarily due to the construction technique that utilizes only a single laser cut for trimming.

The LR series is practically inorganic in construction, making it extremely fl ame-resistant. Components are copper thick fi lm printed onto a high alumina ceramic substrate. The only element

that prevents the part from being totally inorganic is the very small amount of blue-colored epoxy overcoating. This material is very

fl ame-resistant, and is UL-rated for fl ammability with a UL94-V-0 rating. ☛


Even though the LRF3W series and SC-3 look they same, they have different esistance values. The LRF3W and SC-3 products are both made with the same base materials: alumina ceramic substrate, copper end terminations along the long end of the part, and epoxy overcoat. While the resistor material is a different formulation in order to achieve the corresponding difference in respective resistance ranges, the true reason is due to the applications for which each was designed. Because of its low resistance, the LRF3W are used for current sensing, whereas the SC-3 is usually used for more general purpose applications, such as inrush current limiting or withstanding pulse.

SC3 Series – Surface-MountLooking to make the most out of your board space? Check out the SC3 series. This product offers a three watts handling power in a one watt package for high-power dissipation applications. Values range from 1 ohm to 1000 ohms and a one percent absolute tolerance, making this a very popular package.

D2PAK – Surface-mount (New)Providing design engineers with superior heart dissipations in a surface-mount metal-tab package. The D2-style (TO-263) is a power resistor using a proprietary highly reliable copper thick fi lm and alloy resistors on an alumina ceramic substrate. These economical, non-inductive resistors are rated for 25 watts at 25°C case temperature, making them ideal for a variety of surface-mount power applications, where exceptional power performance in a low-profi le package is required. The D2PAK Series resistors offer resistance rages from .02 to 1000 ohm with tolerances to ± 1% and TCRs as low as 100ppm/C.

TFP – TO220 Power Resistor - Thru Hole (New)One of the newest current sensing product offerings from TT/IRC is the TFP series. This product is the same basic design as the D2PAK but comes in a thru-hole styled package. This product is rated at 20 W and has special features such as the non-inductive metal tab design and low thermal resistance. With values ranging from .01 to 1000 in tolerances of one percent, fi ve percent or 10 percent, they are ideally suited for a multitude of industrial applications.

Other Current Sensing Products (New)This is just a sampling of our current sensing products. Call your local TTI offi ce for information on some of our other products such as the OARS, which is our open-air current sensing resistor or perhaps the CSS series which is a one watt product available in ultralow ranges. We also have a complete offering of thru-hole current sensing products in many wattages and ranges.

ConclusionIRC/TT Electronics is your complete source for current sensing products. We are large enough to meet quick delivery requirements or demanding schedules and yet small enough to provide the kind of quality and caring service you deserve. You will fi nd that working with TTI to obtain your IRC/TT products is an effi cient and cost-effective way to get what you want, when you want it.

Engineering KitsIRC has an engineering kits available in its current sensing LR/LRF product line. For information on these kits and how to order them, see page 11. ❖


High Quality Parts, Superior Service & Competitive Prices A world-class passive component supplier, KOA-Speer has dedicated signifi cant resources to developing new products, placing them at the forefront of the industry’s constant push for smaller high quality components. KOA has put great emphasis on improving and expanding its current sensing product offering. KOA-Speer’s current sensing components include thick fi lm, surface mount, molded, metal alloy, metal plate and four-terminal resistors. Its state of the art manufacturing facilities allows the company to take cutting-edge designs to market with short lead times. The combined warehousing and distribution systems of KOA and TTI ensure that components are available upon customer demand.

SL and TSL SeriesOur surface mount molded products include the SL and TSL series. These molded resistors are ideal for power applications including battery packs and power supplies. Available in one, two and three watt packages, they offer excellent dimension accuracy, easing in mounting and shock resistance. These surface-mount components have a fl ameproof (UL94-V-0) molded polymer case and are suitable for fl ow, refl ow and hand-soldering. The TSL offers the same basic one watt component in a lower profi le.

SR73 SeriesThe SR73 family of products is a longtime staple of many current sensing users. These low-ohm, thick fi lm components use an Ru02 thick fi lm resistor element. Anti-leaching nickel barrier terminations come standard 90/10 solder-plated and are also confi gured with a lead-free termination. The SR 73s are built to meet or exceed EIA 575, EIA PDP-100 and MIL-R-55342F standards. These cost-effective parts come in case sizes of 0402, 0603, 0805, 1206, 1210, 2010 and 2512. Tolerances from 1 percent to 5 percent and values from .03 to 9.1 ensure they are useful in a wide range of applications.

LR72 SeriesLR72 surface mount resistors are designed for less thermal expansion and contraction and minimize current interface. LR72A/B/C offers a standard tolerance of ± 5 percent and an inductance value of less than 10nH. They offer a standard resistance value of 2m and have solderable pads that are 60/40 SnPb plated. The LR72 series

may be used in current sensing, low inductance, feedback, surge, pulse and AC applications.

CSR SeriesKOA’s CSR series is a four-terminal current sensing resistor that

offers extremely low resistance values of 5mΩ~50mΩ. This robust component is available for high precision applications in a .5 percent or a one percent tolerance. They also have a low TCR of ± 50ppm and meet the fl ameproof requirements of UL94-V-0. Available in a one watt and a two watt rating, the CSR is ideal for use in electric automobiles and industrial robots. ☛

CSR Series


NPR SeriesThe NPR surface-mount molded current sensing resistor is a non-wire wound structure with metal plate terminals. They are fl ame-retardant (UL94-V-0) and were designed as current detecting resistors for switch mode power supplies and motor controlling circuits for automobiles. This series is available in tolerances as low as one percent and a resistance range of 9.1 mΩ ~ 22 mΩ.

NPR1 SeriesThe KOA NPR1 metal plate current sensing resistor offers an ultralow resistance from 1 mΩ ~ 4 mΩ and have tolerance options of one percent and fi ve percent. This metal alloy resistor features superior corrosion and heat resistance. They are ideally suited for detecting high currents in applications such as CPU, DC/DC dividers and inverted power supplies.

New Products AvailableTLR SeriesRecently arrived on the market is the KOA TLR series of metal plate chip resistors. These provide superior corrosion and heat resistance and the TLR3A is confi gured as a one watt in a 2512 package and is available in 1mΩ, 2mΩ, 3mΩ and 4mΩ ohms. The TLR2B is a .5 watt in a 1206 package and is available in values from 2mΩ to 20mΩ. They are both available in one percent and fi ve percent tolerances, and are an excellent choice for use in DC/DC converters, as well as for many other applications.

UR73 SeriesThe UR73 product line is a complementary line to the SR73 type current sensing resistor product, offering improved Total Current Resistance (TCR) to 100 ppm by the use of a special thick fi lm paste. This line is available in both 0805 and 1206 sizes, and completes our current sensing resistor product expanding into the precision division of these products.

Engineering KitsKOA-Speer has an extensive range of engineering kits available in its current sensing product line. Individual kits are available on the following series of products: SL1, SL2, TLR, UR73, SR731E, SR731J, SR732A, SR732B, SR732E, SR732H, and SR733A. For information on these kits and how to order them, see page 11. ❖

Engineering Kits


At the Forefront of TechnologyVishay is a world leader in current sensing products, offering a range of products that is unmatched in the industry today. Considered to be at the forefront of this technology with a patented Power Metal Strip® process, Vishay also offers molded surface-mount products using wirewound and metal fi lm technologies, as well as the open-air style. With the introduction of new products and continuous efforts to expand and broaden current offering you are sure to fi nd what you looking for in the Vishay family of products.

Power Metal Strip® Product FamilyVishay’s state-of-the-art Power Metal Strip® family of products offers superior performance in high temperature applications. They are available in a wide range of package sizes from an 0805 package to a 4527, with values ranging from .0005 to 1.0 ohm. In addition, they have excellent overload capabilities (equivalent to wirewound) and temperature coeffi cients as low as 30 ppm/°C in some series.

WSL SeriesThe WSL series takes the lead in the Vishay Power Metal Strip® offering. These high power surface-mount devices are ideal for all types of current sensing, voltage division and pulse applications including switching and linear power supplies, instrument and power amplifi ers. This proprietary processing technique produces extremely low resistance values. The specially selected and stabilized materials allow for high power rating. They have the added benefi t of very low inductance (.5nH to 5nH), along with excellent frequency response

capabilities and low thermal EMF. They have a solid metal nickel-chrome or manganese-copper alloy resistive element and an all-welded construction package.

The Vishay Dale WSL series provides an extremely low value with one resistor. This saves mounting costs and space, and improves the MTFB of the DC/DC converter. In comparison, with conventional cermet chips, four to six chips are needed to achieve very low ohmic values. With conventional thin fi lm chips, at least two chips are needed due to their low power capability Vishay Dale® sense resistors provide the

characteristics required and demanded by DC/DC converter operations that cannot

be met with other conventional cermet and thin fi lm resistive chip components.

The core component offerings begins with the WSL0805, which is a .125 watt, with a resistance range of .01 to .2 ohms, a TC of ±75 ppm and are available in with a tolerance of one percent or .5 percent. The WSL1206 (.25 watt), WSL2010 (.5 watt) and WSL2512 (one watt) round out the series with values as low as .001 ohm and as high as .5 ohm. The temperature coeffi cients range from ± 275 to ± 75 ppm/°C. ☛

characteristics required and demanded by


For more power in a smaller size, the WSL high power version is available as the WSL0805-18 (.25 watt), WSL1206-18 (.5 watt), WSL2010-18 (one watt) and the WSL2512-18 (two watts). They have a standard temperature coeffi cient of ± 75ppm, tolerances of one percent and .5 percent, and come in a value range of .001 ohm to a .5 ohm.

Next is the Power Metal Strip® Flip Chip, which is an extended range version and is denoted as the WSL-E series. This series represents the industry’s lowest TCR rating of 15 ppm/°C. This product uses a fi llet-less fl ip chip technology for spacing saving (reduction of mounting occupation area). It is an excellent surface-mount alternative for low-power, leaded wirewound resistors. They have good overload and pulse-handling capabilities (fi ve time rated power for fi ve seconds) with the added benefi t of no noise and no voltage coeffi cient. These chips provide excellent stability in a multitude of different environmental conditions. This fl ip chip comes in three sizes, the WSL1506E (.25 watt), the WSL2010E (0.5 watt) and the WSL2512E (one watt). They are available in a resistance range of .5 ohm up to 10,000 ohms in a one percent or a .5 percent tolerance.

Lastly is the WSL3637 series. This is a low value, four terminal surface-mount product rated at three watts. It has a resistance range of .001 ohm to .01 ohm and has a temperature coeffi cient of ± 50 ppm/°C. The special four terminal design allows for a .5 percent tolerance down to .003 ohms. They are ideal for all types of current sensing, voltage division and pulse applications, including switching and linear power supplies, instruments and power amplifi ers. They have a solid metal nickel-chrome or manganese-copper alloy resistive elements and are encapsulated with a high temperature coating along with electroplated 60/40 tin/lead copper terminations. They also offer very low inductance of .5nH to 5nH and excellent frequency response.

Vishay also offers a one watt version of the four terminal Power Metal Strip® resistor in its WSK2512 product. Touting the same features as the three watt version, the WSK2512 is able achieve a .001 ohmic value in a one percent tolerance and .003 ohmic value in the .5 percent. The component has a temperature coeffi cient ± 35 ppm/ºC for values from .005 to .025 ohm, ± 75ppm/ºC from .003 to .0049 ohms and ± 250ppm/ºC for .001 to .029 ohms. This particular product is electroplated with 100 percent tin, and is compatible with lead and lead-free assembly processes.

Finishing up the Power Metal Strip® offering are the WSR-2, WSR-3 and WSR-5 series. This unique series offers the power of a fi ve watt and three watt component in a two watt (4527) package. They feature the same molded high temperature encapsulation and all welded construction seen in several other Vishay series. They also have a solid metal nickel-chrome or manganese-copper alloy resistive element, 60/40 tin/lead copper terminations, low thermal EMF and very low inductance and with excellent frequency response. ☛

watt) and the WSL2512-18 (two watts). They have a standard temperature


SMD Power Metal Film ProductsThe Vishay WSF series was designed using existing metal fi lm technology to create a surface-mount power resistor. The special features of this product included molded encapsulation, wrap around (SnPb) electroplated terminations and high power ratings. This product exhibits excellent stability in a multitude of different environmental conditions. The WSF2012 is a 0.5 watt component with an epoxy encapsulation. Available from 5.0 ohms to 1.43K ohms. The WSF2515 is the one watt version with ranges from 25.6 ohm to 10K ohms. The two watt component is the WSF4527 and has a value range of 10 ohm to 100k ohms. All of these components have a standard temperature coeffi cient of ± 100ppm but are also available in a 50 ppm or a 25 ppm version.

SMD Wirewound – Precision PowerThe Vishay SMD wirewound family of products is an industry staple. They are available in power rating from .5 watt to 3 watts. The special features of these components include all welded construction, superior surge capabilities and high power ratings. They have wrap around (SnPb) electroplated terminations. The WSC-1/2, WSC-1 and WSC-2 series are epoxy encapsulated and the newer versions (WSC2515, WSC4527 and WSC6927) utilize thermoplastic encapsulation. They are also available in a non-inductive version, the WSN prefi x, with Aryton-Perry winding. The maximum resistance value for the non-inductive product is one-half the WSC range. These products are used heavily in the instrumentation and automotive controls markets, as well as in voltage divider circuits and telecommunications applications.

Special Designs Vishay has recently introduced two new products adding to their already superior line-up of current sensing products. First is the WSZ series. This product is the perfect low-cost, high power answer to through-hole replacement. They can be used to replace axial-leaded components without increasing the board temperature. The WSZ6720 is a cement-encapsulated resistor with a 1.8 watt rating. For more power, look to the silicon encapsulated WSZ7532 series, which is rated at 3.75W. Both of these products are available in one percent to 10 percent tolerances with temperature coeffi cients as low as to 30 ppms.

The SR5 product series is an open-air style resistor for through-hole applications. This high power fi ve watt device helps to maintain a low board temperature by keeping the resistive element away from the board. The SR5 is available in one percent and fi ve percent tolerances. The ultralow value range of .004 ohm to .05 ohm make them a valuable asset in many applications, including motor starting, instrumentation, power supplies and switching circuitry.

Engineering Kits AvailableVishay manufactures an engineering kit for their Power Metal Strip® products, for more information see page 11. ❖


World Class Component QualityThe Electronics Components Division of the Panasonic Industrial Company is one of the industry’s largest suppliers. A wide product offering, coupled with global manufacturing and sales capabilities, and a commitment to customer service make Panasonic a preferred vendor to the world’s most famous equipment manufacturers of high-tech electronic products. Choosing Panasonic means more than selecting a name you know and trust. It means choosing the best quality components the industry can offer. Panasonic has a variety of products specifi cally designed to meet the needs of today’s current sensing applications.

ERJ-M1W Surface-mount The ERJ-M1W series leads the Panasonic offering in current sensing products. This robust product comes in an industry standard 2512 size package and has a one watt power rating. The features include ultralow resistance values, down to one mOhm or three mOhms and higher with high precision specifi cations. A low profi le, low inductance, and strong body design make it a perfect fi t for many applications. Suitable for fl ow and refl ow soldering, they are available from 0.003 to 0.020 ohms in a ±1percent tolerance or 0.001 to 0.020 ohm in ± 5 percent tolerance.

Features Include:• Precision production control of resistance values using four probe (Kelvin connection) measuring technique• High heat dissipation• Low residual reactance• Low profi le, high strength construction

ERJ-L Surface-mountThe ERJ-L series is a high reliability product using a metal glaze thick fi lm resistive element and three layer electrodes. These are available in a wide variety of sizes and values.

ERJ- R Surface-mountThe ERJ-R series complets the Panasonic offering. These components are ideal for applications requiring slightly higher resistance values. Sizes include 0603, 0805, 1206, 1210, 1812, and 2512s. Values range from 0.1 to a 9.1 ohm in ±1 percent and ±5 percent tolerances. Small and lightweight, they use high reliability metal glaze thick fi lm resistive elements and three layer electrodes. They are compatible with pick and place equipment and are suitable for refl ow and fl ow soldering.

For those current sensing applications that use the FET on resistance (Rds on) and require temperature compensation instead of current sensing resistors, Panasonic offers both NTC thermistors (ERT-J) and linear PTC thermosensitive chip resistors (ERA-S 0.1W, ERA-V 0.06W series).

ERT-J Surface-mountPanasonic presents multilayer negative temperature coeffi cient (NTC) chip thermistors in case sizes including 0402 and

0603 in the wide operating temperature range of –40 to +125°C. These also are suitable for fl ow and refl ow soldering.

ERA-S, ERA-V Surface-mount Panasonic offers new thermosensitive chip resistors that are linear positive temperature coeffi cient (PTC) devices ERA-S in an 0805 case size and ERA-V in an 0603 in the wide operating temperature range of –40 to +125°C, and temperature coeffi cients of resistance (TCRs) ranging from 1000 to 4700 (EIA E12 series values)

with resistance tolerance of ±5percent. These linear response devices, with fast response to temperature change, facilitate temperature compensation designs. ❖


Glossary

Ambient Operating Temperature: The temperature of the air surrounding an object, neglecting small localized variations.

Ampere: Unit of measure for electrical current.

Bulk Resistor: A resistor made by providing ohmic contacts between two points of a homogenous, uniformly doped material.

Chip Resistor: A small rectangular resistor chip used in hybrid integrated circuits and available in either thick film or thin film construction.

Circuit: An interconnection of components that forms a complete path for the controlled flow of electrical current.

Clean Room: A special manufacturing area where the air is filtered to remove dust particles and precautionary measures are used to keep contamination away from the unprotected circuit during processing.

Current: (unit Amp):Flow of electrons, measured in amperes. One ampere will flow when one volt is provided to a circuit which has a resistance of one ohm. The rate of the flow of electrons in the circuit.

Derating: At ambient temperatures higher than the maximum specified for full rated power, a reduced amount of power is allowable in the resistor. The allowable amount is shown in derating curves which normally end at zero power at the maximum surface temperature applicable to the resistor type.

Dielectric Strength: The maximum voltage of the dielectric or insulation of a resistor or potentiometer applied between the case and all terminals connected to each other, without exceeding a specified leakage current.

Discrete Resistors: Resistors that have a single resistive element per component.

Film Resistor: A fixed resistor relying on film properties of resistance material rather than bulk properties.

Fixed Resistors: Resistors that have a specified resistance value that does not change.

Flip Chip Resistor: An unencapsulated resistor chip on which bead-type leads terminate on one face to permit “flip” (face down) mounting of the resistor chip by contact of the leads with interconnective circuitry.

Frequency: The number of cycles per unit of time of a reoccurring event, wave or oscillation. Usually measured in cycles per second, known as Hertz.

Hot-Spot Temperature: The maximum temperature measured on the resistor due to both internal heating and the ambient operating temperature.

Impedance: The resistance to the flow of current (represented by an electrical network of combined resistance, capacitance, and inductance reaction) in a conductor as seen by an AC source of varying time voltage measured in ohms.

Inductance: The property of a wirewound resistor that causes voltage to be set up because of a change in current through the device.


Insulation Resistance: The DC resistance measured between all terminals connected together and the case, exterior insulation, or external hardware.

Insulator: A material along which an electrical charge (current flow) cannot readily pass. Used to keep conductors apart or to prevent the escape of electricity.

Linearity: The relationship of actual electrical output to the theoretical output when the theoretical output is a straight-line function.

Low Profile: Components designed with “lower than standard heights,” to save space and allow clearance when mounted on PCB’s.

Maximum Working Voltage: The maximum specified voltage that may be applied across a resistor.

Megohm: A million (106) ohms.

Metallization: A film pattern (single or multilayer) of conductive material deposited on a substrate to interconnect electronic components, or the metal film on the bonding area of a substrate which becomes a part of the bond and performs both an electrical and a mechanical function.

Ohm’s Law: The formula used to determine the three basic building blocks of a circuit: volts (V), current in amps (I), resistance in ohms (R); V = I x R.

Output: The voltage, current, or power developed by a circuit in response to an input.

PPM: Parts per million. The terminology used when describing the temperature coefficient.

Passive Components: Components such as capacitors and resistors, which have no gain characteristics.

Paste/Ink: Screenable, thick film material composed of metals, oxides, and glasses in an organic vehicle which when fired, produces a circuit element such as a resistor or conductor.

Power Rating: The maximum specified power that can be dissipated in a resistor under specified conditions of mounting and environment. The maximum heat a trimmer can dissipate across the resistive element under specified conditions. Specified in units of watts or milliwatts (thousandths of a watt).

Reactance: Opposition to the flow of alternating current offered by capacitance, inductance or both. Both reactances are measured in ohms, and symbolized by the variable x.

Resistance: A specific property of a material depends on its molecular structure, size and temperature and in a circuit, acts to oppose an applied voltage and limit the current flowing into the circuit. Resistance is measured in ohms.

Resistive Products: A broader term that describes components whose primary function is to introduce resistance into the circuit.

Resistor Element: A continuous, unbroken length of resistive material without joints, bonds or welds except at the junction of the element and the electrical terminals connected to each end of the element, or at an intermediate point.

24 C u r r e n t S e n s i n g R e s i s t o r s

Resistor: A basic component that introduces resistance in electrical and electronic circuits.

Resistor Tolerance: The permissible deviation of the manufactured resistance value (expressed in percent) from the specified nominal resistance value at standard (or stated) environmental conditions.

Screen: The process of printing a network pattern of thick-film ink or paste onto a substrate by means of a squeegee applied to a photo-etched wire-mesh “silk screen” or metal mask.

SMT/SMD: Surface-mount technology/surface-mount device.

Stability:The overall ability of a resistor to maintain its initial resistance value over extended periods of time, when subjected to any combination of environmental conditions and electrical stresses.

Standard Resistance Value: The resistance value tabulated by a decade chart is specified in the applicable military specification. Resistance values not listed in the chart for the appropriate tolerances are considered as non-standard for that specification.

Surface Mount: See SMT/SMD

Temperature Coefficient (resistance temperature characteristics): The magnitude of change in resistance due to temperature; usually expressed in percent per degree Celsius or parts per million degree Celsius (ppm/°C).

Tolerance: Usually applies to the extent from which the actual resistance reading may vary from the rated resistance value when it is actually tested.

Tracking: The inherent capability of resistors from the same formulation and screened onto the same substrate to exhibit similar performance characteristics (e.g., drift, TCR).

Voltage (unit V):The electromotive force trying to move electrons from negative to positive; the “pressure” in the circuit.

Watt: Practical unit of electrical power. One watt is the power delivered when a current of one ampre is driven by one volt.

Wirewound Resistor: A resistor in which the resistance element is a length of high-resistivity wire or ribbon, wound onto an insulating core, then encapsulated in a vitreous enamel, silicone or cement compound.

Zero Ohm Resistors: Products that look like resistors, but actually have no resistance and instead perform as jumpers.

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