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INTRODUCTION
Chassis Plans' XPT single board computer, model number S6090,
uses a unique cooling solution designed to provide
reliable system operation at elevated ambient
temperatures. Many of today’s Single Board Computer cooling solutions
leave damaging processor-generated heat in the
chassis and rely on the system fan or fans for
removal. Also, heat generated by other Single Board Computer components
is often simply radiated into the system enclosure.
The XPT’s cooling solution is designed to prevent
a premature system failure or a temporary shutdown
situation by cooling the Intel® Xeon™
processors, and other Single Board Computer components, while channeling
the heated air out of the chassis. The net result
is an effective Single Board Computer cooling solution that maximizes
system up time leading to more efficient operation
with faster return on investment.
BACKGROUND INFORMATION
It’s an engineering fact of life that as silicon-based microprocessors
increase their operating speeds, the resultant
power consumption also increases. Compounding
this situation is the fact that as the processor’s
speed increases, the allowable processor case
temperature (Tcase) decreases. With today’s Xeon
processors, cooling systems must be designed around
a maximum power dissipation of 101 Watts with
a maximum Tcase rating of 73° Celsius. In the
XPT the dual Xeon processors can theoretically
dissipate up to 202W. The power needed to drive
these processors demands voltage regulation circuitry,
i.e. VRMs, that also generates heat. Other Single Board Computer
components such as the chipsets, bridges, SCSI,
video and Ethernet controllers generate additional
heat, so the design engineer must have a plan
to effectively manage and control Single Board Computer board temperature
in order to maximize system reliability and value.
The XPT cooling solution cools all of the Single Board Computer
components, not just the processors.
DESIGN REQUIREMENTS
The prime engineering directive forChassis Plans' XPT cooling
solution was to design a system that allowed the
Single Board Computer to be specified and validated for operation
at a maximum ambient temperature of 45° C. This
validation was to be performed under a variety
of high temperature and system loading conditions,
and the cooling solution needed to have a safety
margin of several degrees. These design requirements
pointed to a solution that cools all Single Board Computer components
while aiding in the removal of heat from the chassis
enclosure. Figure 1 shows the XPT’s major heat-producing
components.
The XPT cooling solution effectively
maintains proper thermal operating conditions
for these components in the smallest package possible
in order to maximize Single Board Computer reliability in a wide
variety of applications.
Figure 1
OVERVIEW
Figure 2 shows two views of the
XPT, i.e. one with the cooling solution installed
and one with it removed, in order to show the
key components of the assembly.
 Figure 2
The voltage that drives the dual
speed fan is controlled by a thermal switch/sensor
located on the XPT’s I/O board. Single Board Computer board temperatures
are much higher than external ambient temperatures.
The switch delivers maximum voltage to the fan
when the sensor portion of the device reads a
board temperature over 48° C. This causes the
fan to operate at a maximum speed of 50 CFM. Under
normal operating conditions, the fan operates
at approximately 37 CFM. Running the fan at full
speed only when necessary maximizes fan reliability
and MTBF. An air deflector is used to direct a
small amount of cooling air over the XPT’s VRM
and I/O board components. Board stiffeners are
used to provide support and minimize board flexure.
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MECHANICALS
Figure 3 illustrates how the XPT,
with the cooling solution installed, fits into
a typical PICMG® backplane.
 Figure 3
The XPT’s cooling solution accommodates
the placement of half-size PCI cards approximately
2.3” (58.4mm) away from the Single Board Computer. Full-length cards
must be placed approximately 3.2” (81.3mm) away
from the XPT.
AIR FLOW
Cool air is drawn through the
front of a typical enclosure chassis and into
the XPT’s shroud by the dual speed fan. The cool
air warms as it passes over various Single Board Computer components
and is exhausted through the I/O bracket as shown
in Figure 4.
 Figure 4
The shape of the XPT’s shroud
is designed to maximize the air flow over critical
Single Board Computer components. An air deflector is part of the
shroud and directs low pressure cooling air between
the two boards in the XPT single board computer.
Figure 5 illustrates the direction of the air
movement through the XPT’s shroud.
 Figure 5
The passive heat sinks mounted
on top of the Xeon processors have a height differential
of 10mm in order to ensure that both processors
are adequately cooled. The difference in the heights
of the passive heat sinks can be seen in Figure
2. Some cooling air is directed over the VRM circuits
in order to maintain optimum performance during
peak power demands.
SUMMARY
The cooling solution on the XPT
single board computer maximizes system reliability
by effectively cooling the Single Board Computer while aiding in
the removal of heat from the enclosure. In the
future, microprocessors will continue to increase
in speed and power consumption, leading to increased
heat dissipation. Newer manufacturing processes
have the potential of changing this dynamic; however,
these improvements will not change the basic fact
that faster processors will always run hotter.
Chassis Plans' engineers will continue to design
innovative cooling solutions for the processors
and other SBC board components which are required
for demanding applied computing environments.
Intel and Xeon are trademarks
of Intel Corporation.
All other product names are trademarks of their
respective owners.
Copyright
® 2003 by Chassis Plans, LLC.
All rights reserved.
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