LPS 800
www.vishay.com
Vishay Sfernice
Revision: 01-Aug-13
2
Document Number: 50054
For technical questions, contact: sferfixedresistors@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
RECOMMENDATIONS FOR MOUNTING ONTO A HEATSINK
• Surfaces in contact must be carefully cleaned.
• The heatsink must have an acceptable flatness: From 0.05 mm to 0.1 mm/100 mm.
• Roughness of the heatsink must be around 6.3 μm. In order to improve thermal conductivity, surfaces in contact (alumina,
heatsink) should be coated with a silicone grease (type SI 340 from Rhône-Poulenc or Dow 340 from Dow Corning) or a
thermal film (type Q Pad II) easier and faster to install than the grease.
• The fastening of the resistor to the heatsink is under pressure control of two screws tightened at 2 Nm for full power
availability.
• The following accessories are supplied with each product:
- 2 screws CHC M4 x 25 class 8.8 and 2 M4 contact lock washers for heatsink mounting
- 2 screws TH M4 x 6/6 and 2 M4 contact lock washers for connections.
CHOICE OF THE HEATSINK
The user must choose the heatsink according to the working conditions of the component (power, room temperature).
Maximum working temperature must not exceed 175 °C. The dissipated power is simply calculated by the following ratio:
P: Expressed in W
T: 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: (see specifications environmental paragraph).
R
TH (c - h)
: Thermal resistance value measured between outer side of the resistor and upper side of the heatsink.
This is the thermal resistance of the interface (grease, thermal pad), and the quality of the fastening device.
R
TH (h - a)
: Thermal resistance of the heatsink.
Example:
R
TH (c - a)
for LPS 800 power dissipation 180 W at + 50 °C room temperature.
T 175 °C - 50 °C = 125 °C
R
TH (j - c)
+ R
TH (c - h)
+ R
TH (h - a)
= = = 0.69 °C/W
R
TH (j - c)
= 0.112 °C/W
R
TH (c - h)
+ R
TH (h - a)
= 0.69 °C/W - 0.112 °C/W = 0.578 °C/W
PERFORMANCE
TESTS CONDITIONS REQUIREMENTS
Momentary Overload
IEC 60115-1
1.5 x P
r
/10 s
U
max.
U
L
= 5000 V
± (0.25 % + 0.05 )
Rapid Temperature Change
IEC 60115-1/IEC 30068-2-14 Test Na
50 cycles
- 55 °C to + 175 °C
± (0.5 % + 0.05 )
Load Life
IEC 60115-1
1000 h (90/30) P
r
at 85 °C
± (0.5 % + 0.05 )
Humidity (Steady State)
IEC 60115-1
56 days RH 95 %/40 °C
± (0.5 % + 0.05 )
Vibration
MIL STD 202 method 204 cond. D
(10 g; 5/500 Hz)
± (0.25 % + 0.05 )
Climatic Sequence
IEC 60115-1
(55/175/56)
± (1 % + 0.05 )
Tightening Torque on Heatsink
LPS 800
2 Nm
P
T
R
TH (j - c)
R
TH (c - h)
R
TH (h - a)
++
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