APPNOTESMP9100 [ETC]
Understanding the Power Rating of Caddock MP9100 Resistors; 了解额定功率Caddock产品种类MP9100电阻
| 型号： | APPNOTESMP9100 |
| 厂家： | 
ETC |
| 描述： | Understanding the Power Rating of Caddock MP9100 Resistors |
| 文件： | 总2页 (文件大小：23K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
CADDOCK
Applications Engineering Note: AEN-0102
Release Date: 9/20/02, Rev. A, Rev. Date: 9/20/02
Page 1 of 2
Understanding the Power Rating
of Caddock MP9100 Resistors
Understanding the Power Rating
terial characteristics and ambient temperature, (TA). The
maximum continuous power rating (100 Watts) for the
Caddock MP9100 resistor is based on a case tem-
perature (TC) of 25°C measured at the center of the
exposed ceramic surface. The Caddock MP9100 re-
sistor has a thermal resistance of 1.5°C/watt (RØJC),
from the junction (resistor film) to the case (exposed
ceramic case interface). For a case temperature (TC)
above 25°C, derating is necessary.
The maximum power rating of the Caddock MP9100
(TO-247 type) resistor is specified with the ceramic
surface maintained at 25°C using the same method
established and proven by power semiconductor
manufacturers over many years.
Caddock’s careful design practices and thorough re-
liability testing assure the user that the part will per-
form to all published specifications as long as its case
temperature (TC) does not exceed that specified in
Figure 1. Surge ratings must be observed.
Allowable power dissipation (PD, watts) may be deter-
mined by the following equation.
TJ - TA
Equation 1 PD =
(RØJC + RØCS + RØSA
)
MP9100 Derating Curve
100 %
80 %
60 %
Using the information provided in Fig 2, allowable
power dissipation and temperature gradients can be
estimated. Typical thermal resistance of various ma-
terials can be found in Table 1 on the next page. It
should be noted that material characteristics are those
provided by the manufacturers and these can vary
greatly if careful manufacturing processes are not ob-
served. Caddock suggests that actual temperature
measurements should be made under worst case con-
ditions to assure maximum reliability of a design.
Figure 1
40 %
20 %
0
25
100
175
Case Temperature (T , °C)
C
In high power applications, the actual power dissipa-
tion capability of the resistor will be greatly depen-
dent on the heat sink, mounting method, interface ma-
Center Line through Center
of Ceramic Element
Figure 2 MP9100 with Mounting Screw
and Belleville Washer
Mounting Screw
Belleville Washer
T
Resistor Film Temperature (Max. 175°C)
J
Detail of
Cross Section
R
Thermal Resistance - Resistor Film
ØJC
to Exposed Ceramic Case Interface
Thermal Grease
or Pad
T
Case Temperature (Exposed Ceramic Surface)
C
R
Thermal Resistance - Case to Heat Sink
ØCS
Surface (Pad or Thermal Grease)
PD
Heat Sink
(mounting surface)
T
Heat Sink Temperature
S
R
Thermal Resistance - Heat Sink to
ØSA
Ambient Air or Reference Temperature
T
Ambient or Reference Temperature
A
CADDOCK
© Caddock Electronics, 2002
A copy of this Application Note can be obtained at www.caddock.com
Applications Engineering Note: AEN-0102
Page 2 of 2 - Rev. A
Calculation Examples
Mounting Configurations
Using Equation 1 and data from Table 1, the allow-
able power can be determined for given ambient con-
ditions. Assuming a maximum ambient air tempera-
ture of 50°C with the part mounted using thermal
grease on an aluminum chassis, the allowable power
can be calculated from Equation 1 as follows:
Mounting pressure, surface cleanliness, surface flat-
ness and surface finish are just a few of the variables
which can have considerable effect on temperature
rise and power dissipation. Caddock recommends an
ideal spring mounting force of 4 to 15 pounds, or a
typical mounting screw torque of 6 to 8 in - lbs which
should provide 150 to 300 pounds of force. If a screw
is used, Caddock recommends the use of a good ther-
mal grease in conjunction with a #6 Belleville washer
compressed to 50% of its normal height. These wash-
ers (p/n 04CSB52200F004) are available from Ari-
zona Hydrogen, phone number 602-275-4126.
TJ - TA
(RØJC + RØCS + RØSA
PD =
)
175°C- 50°C
(1.5°C/W + 0.5°C/W + 2°C/W)
PD =
125°C
4°C/W
PD =
PD =
Table 1 Typical Thermal Resistance of Various
Materials Used for High-Power Designs with
Caddock MP9100 Resistors
31.25 watts
The same part, mounted on a water cooled heat sink
providing a constant 50°C reference temperature, will
dissipate more than twice this amount of power.
R
(°C/W)
Resistor Type
ØJC
Caddock MP9100 (junction to case)
1.5
175°C- 50°C
(1.5°C/W + 0.5°C/W)
PD =
R
(°C/W)
Interface Material (thickness)
ØCS
Solder (0.010”)
0.1
PD = 62.5 watts
Epoxy (0.010”)
1 0
2.5
Filled Epoxy (0.010”)
Thermal Grease (0.003”)
Surge and Pulse Ratings
0.5 to 2
Q-Pad II (0.006”)
0.9
3.1
1.7
Surge or pulse voltages can be a factor in design reli-
ability. The following guidelines should be followed.
SIL-PAD 400 (0.007”)
SIL-PAD 2000 (0.015”)
Thermal Clad ® dielectric (0.003”)
0.4
1. Do not exceed 750 volts peak.
FR-4 / G-10 printed-circuit
board (0.063”)
20 to 65
2. Use the following guidelines for maximum pulse en-
ergy of a single pulse.
0.1
0.06
0.5
Aluminum (0.063”)
Copper (0.063”)
Pulse Width
Energy (1 J = 1 Watt second)
Steel (0.063”)
10 µsec
100 µsec
1 msec
10 msec
100 msec
0.07 J
0.25 J
0.90 J
3.5 J
0.36
0.1
96% Alumina (0.030”)
Aluminum Nitride (0.030”)
Beryllia (0.030”)
0.05
15 J
Typical Mounting Surfaces
to Ambient Air
R
(°C/W)
ØSA
7" X 5" X 2" 0.040"
Aluminum chassis
3. Accumulated pulse energy delivered in each sec-
ond should not exceed allowable average power. De-
rate the pulse energy using the Derating Curve (Fig-
ure 1) based on estimated case temperature.
2
Small Finned Sheet Aluminum
heat sink (convection)
2 0
Small Finned Sheet Aluminum
heat sink (200 LFM Airflow)
1 0
4.5" X 3" X 3" Mult-Finned
4. Above 100 msec to 5 seconds, the overload rating
is 1.5 times the allowable power of the resistor in the
application.
1.5
Extruded Aluminum (convection)
4.5" X 3" X 3" Mult-Finned
Extruded Aluminum (200 LFM)
0.8
CADDOCK
© Caddock Electronics, 2002
A copy of this Application Note can be obtained at www.caddock.com
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