User guide

RTO 20
Power Resistors, Thick Film Technology
Vishay Sfernice
Document Number: 50005 For technical questions, contact: [e-mail]
www.vishay.com
Revision: 24-Nov-08 15
Note
• For very low ohmic values, TCR for information
CHOICE OF THE HEATSINK
The user must choose according to the working conditions of the component (power, room temperature).
Maximum working temperature must not exceed 155 °C. The dissipated power is simply calculated by the following ratio:
P: Expressed in W
ΔT: Difference between maximum working temperature and room temperature
R
TH (j - c)
: Thermal resistance value measured between resistive layer and outer side of the resistor. It is the thermal
resistance of the component: (Special Features table)
R
TH (c - a)
: Thermal resistance value measured between outer side of the resistor and room temperature. It is the thermal
resistance of the heatsink itself (type, shape) and the quality of the fastening device.
Example:
R
TH (c - a)
:For RTO 20 power rating 10 W at ambient temperature + 25 °C
Thermal resistance R
TH (j - c)
: 6.5 °C/W
Considering equation (1) we have:
PERFORMANCE
TESTS CONDITIONS REQUIREMENTS
Momentary Overload
EN 60115-1
2 Pr 5 s for R < 2 Ω
1.6 Pr 5 s for R ≥ 2 Ω
Us < 1.5 UL
± (0.25 % + 0.005 Ω)
Rapid Temperature Change
EN 60115-1/60068-2-14
5 cycles
- 55 °C to + 155 °C
± (0.5 % + 0.005 Ω)
Load Life
EN 60115-1
1000 h Pr at + 25 °C
± (1 % + 0.005 Ω)
Humidity (Steady State)
EN 60115-1
56 days R.H. 95 %
± (0.5 % + 0.005 Ω)
High Temperature Exposure
NF EN 140 000
1000 h - 40 % Pr at + 100 °C
± (0.5 % + 0.005 Ω)
Vibration MIL STD 202, Method 204 C Test D ± (0.2 % + 0.005 Ω)
Terminal Strength MIL STD 202, Method 211 Test A1 ± (0.2 % + 0.005 Ω)
Shock
IEC 60115-1
IEC 60068-2-27
Saw tooth: 100 g/6 ms
± (0.5 % + 0.005 Ω)
SPECIAL FEATURES
Resistance Values ≥ 0.01 ≥ 0.015 ≥ 0.1 ≥ 0.5
Tolerances ± 1 % at ± 10 %
Typical Temperature
Coefficient Range
(- 55 °C to + 155 °C)
± 900 ppm/°C ± 700 ppm/°C ± 250 ppm/°C ± 150 ppm/°C
P =
ΔT
R
TH (j - c)
+ R
TH (c - a)
[]
-----------------------------------------------------------
1()
ΔT 155 °C - 25 °C 130 °C==
R
TH (j - c)
+ R
TH (c - a)
=
ΔT
P
-------
=
130
10
----------
= 13 °C/W
R
TH (c - a)
= 13 °C/W - 6.5 °C/W = 6.5 °C/W