General Note
IRC reserves the right to make changes in product specifi cation without notice or liability.
All information is subject to IRC’s own data and is considered accurate at time of going to print. A subsidiary of
TT electronics plc
• 4222 South Staples Street • Corpus Christi Texas 78411 USA
Wire and Film Technologies Division
Telephone: 361 992 7900 • Facsimile: 361 992 3377 • Website: www.irctt.com
Open Air
Current Sense Resistors
OAR Series
• TCR’s to ±20ppm/°C
• Power ratings of 1, 3, & 5W @ 85°C
• Resistance range from 2.5mΩ to 100mΩ
• Open air design maximizes thermal performance
• Welded copper leads minimize effects from solder wicking and provide
true 1% performance
Electrical Data
Part
Number
Power Rating
@ 85°C
(watts)
Resistance
Range (mΩ)
Tolerance
(±%)
TCR
(±ppm/°C)
Inductance
(nH)
OAR-1 1.0 3, 5, 10, *20, *25, 50
1, 2¹, 5 20 <10
OAR-3 3.0 2.5, 5, 10, 15, 20, 25, *30, 50, 100
OAR-5 5.0 3, 5, 10, *15, *20, *25, *50
Notes:
¹ ±2% tolerance available <0.005mΩ
* denotes resistance values that may have longer lead times than other values listed
* Please contact factory for resistance values not listed
Load Life (1000 hours @ 25°C) ΔR/R <1%
Moisture (no load for 1000 hours) ΔR/R <1%
Temperature Cycling (-40°C to +125°C for 1000 cycles) ΔR/R <1%
Operating Temperature -40°C to +125°C
Environmental Data
Features:
• Welded construction
• Flameproof
• Inductance less than 10 nanohenries
• Solderable copper leads (60/40) and Lead-Free
Applications:
• Current sensing
• Feedback
• Motor Controllers
• Power Supplies
OAR Series Issue January 2010 Sheet 1 of 3
• 4222 South Staples Street • Corpus Christi Texas 78411 USA
Wire and Film Technologies Division
Telephone: 361 992 7900 • Facsimile: 361 992 3377 • Website: www.irctt.com
Physical Data
Dimensions (Inches and (mm))
IRC Type A B C E F
OAR-1 0.450 +0.040/-0.020
(11.43 +1.020/-0.508)
0.200 ±0.100
(5.08 ±2.54)
0.125 ±0.030
(3.18 ±0.762)
0.065 +0.010/-0.005
(1.65 +0.254/-0.127)
0.040 ±0.002
(1.02 ±0.051)
OAR-3 0.600 +0.040/-0.020
(15.24 +1.020/0.508)
0.600 Typ
(15.3 max.)
0.125 ±0.030
(3.18 ±0.762)
0.065 +0.010/-0.005
(1.65 +0.254/-0.127)
0.040 ±0.002
(1.02 ±0.051)
OAR-5 0.800 +0.040/-0.020
(20.32 +1.020/-0.508)
0.670 Typ
(8.9 max.)
0.125 ±0.030
(3.18 ±0.762)
0.065 +0.010/-0.005
(1.65 +0.254/-0.127)
0.040 ±0.002
(1.02 ±0.051)
Open Air
Current Sense Resistors
B
C
A
E
F
On lower ranges stand-off may be
eliminated
NOTE:
Contact factory for:
1. Variations of “A” dimension.
2. Different lead diameter.
Test Point (Kelvin connection)
The thermal images (not simulations) above are of the OARs products at their respective power rating. Notice the
solder joint temperature is much lower than the hotspot. The unique construction of the OAR isolates the tempera-
ture of the hotspot from the circuit board material preventing damage to the circuit board. Additionally, the thermal
energy is dissipated to the air instead of being conducted into the circuit board potentially causing a nearby power
component to exceed its rating.
The standard test circuit board consists of a four layer FR4 material with 2 ounce outer layers and 1 ounce inner
layers, which is typical of many industry designs. The test conditions were in ambient temperature conditions, ap-
proximately 72 °C with no forced air. Contact IRC for more details or for other thermal image test data for specifi c
resistance values and power levels.
Thermal Image Data
OAR-1 5 mΩ @ 1 Watt
Hot Spot: 87°C
Solder Joint: 45°C
OAR-3 5 mΩ @ 3 Watt
Hot Spot: 160°C
Solder Joint: 70°C
OAR-5 5 mΩ @ 5 Watt
Hot Spot: 230°C
Solder Joint: 96°C
#OPPER
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OAR Series Issue January 2010 Sheet 2 of 3
• 4222 South Staples Street • Corpus Christi Texas 78411 USA
Wire and Film Technologies Division
Telephone: 361 992 7900 • Facsimile: 361 992 3377 • Website: www.irctt.com
Sample Part No.
IRC Style
OAR
Power Rating in Watts
1 = 1W, 3 = 3W, 5 = 5W
Resistance Range
‘R’ indicates decimal point location
Tolerance
F = ±1%, G = ±2%, J = ±5%
RoHS Indicator
LF indicates RoHS compliance
Blank indicates Sn/Pb terminal
tinning; available on special request
Ordering Data
OAR 1 R100 F LF
The typical power derating curves are based on conservative design concepts that extend from fi lm
based products. The OAR is a solid metal alloy construction that can withstand comparably greater
operating power levels than conservative design models permit. Typically the resistive alloys can
withstand temperatures in excess of 300°C. Therefore, system thermal design considerations are a more
signifi cant design parameter due to the heat limitations of solder joints and/or circuit board substrate
materials.
Power Derating
Pulse/Surge Chart @ 50 msec duration
0 10 20 30 40 50 60 70 80 90 100
700
600
500
400
300
200
Resistance (milli-ohms)
Surge Current (Amps)
0
100
OAR-1
0 5 10 15 20 25 30 35 40 45 50
1400
1200
1000
800
600
400
Resistance (milli-ohms)
Surge Current (Amps)
0
200
0 10 20 30 40 50 60 70 80 90 100
1400
1200
1000
800
600
400
Resistance (milli-ohms)
Surge Current (Amps)
0
200
OAR-3 OAR-5
The Surge current charts are approximations of the capabilities of the OAR product and should not be
used to the exclusion of actual testing. The relative high surge currents depicted in the charts are as a
result of the robust all metal welded construction and the heat carrying capability of metal. Additionally
the OAR resistive wire provides large relative cross section for current fl ow as compared to other resistor
technologies, such as thin fi lm, thick fi lm, or metal strip.
Open Air
Current Sense Resistors
OAR Series Issue January 2010 Sheet 3 of 3
