Application Note 653 9
Intel740™ Graphics Accelerator Thermal Design Considerations
4.1.2 Fan Direction
If the fan(s) are not moving air across the graphics processor and the card then little cooling can
occur. Hence, the Intel740 graphics accelerator may exceed it’s absolute maximum thermal ratings.
Note the recommended fan airflow directions in Figure 2 and Figure 3.
The direction of the air flow can also be modified with baffles or ducts to direct the air flow over
the graphics processor. This will increase the local flow over the device and card and may
eliminate the need for a larger or higher speed fan.
4.1.3 Size and Quantity
A larger fan does not always increase cooling efficiency. A small blower using ducting might
direct more air over the graphics card than a larger fan blowing non-directed air. The following
provides some recommendations for the size and quantity of the fans in AGP systems.
• The fan should be a minimum of 80 mm (3.150”) square, with a minimum airflow of
approximately 40 CFM (cubic feet per minute), or approximately 400 LFM (linear feet per
minute). As shown in Figure 2 and Figure 3, two fans are used. The intake air fan blows cooler
external air into the chassis, while the second fan (most likely in the power supply) exhausts
the air out of the system.
• As an example, in a lab test system, graphics card ambient temperatures were reduced by an
average of roughly 10% in an ATX design and 15% in an NLX design by simply adding a
front system fan. In general, the use of two fans benefits the entire system by reducing internal
ambient temperatures. However, as system configurations vary, testing the target
configuration to verify the benefit is recommended.
4.1.4 Fan Venting
As shown in Figure 2 and Figure 3, intake venting should be placed at the front (user side) of the
system. Location should take into consideration cooling of the microprocessor and peripherals as
well as the Intel740 graphics accelerator. A good starting point would be the lower 50% of the
Front Panel (Bezel). Intake venting directly in front of the intake fan is the most optimal location.
4.1.5 Vent Placement
In most cases, exhaust venting in conjunction with an exhaust fan in the power supply is sufficient.
However, depending on the number, location and types of add-in cards, intake or exhaust venting
may be necessary near the cards as well. This is particularly important for the graphics card in NLX
designs as it aids in eliminating dead air space near the AGP Slot (see Figure 3).
Vent placements should be modeled or prototyped for the optimum thermal potential. Hence, a
system should be modeled for the worst case (i.e., all expansion slots should be occupied with
typical add-in options).
4.1.5.1 Vent Area/Size
The area and/or size of the intake vents should consider the size and shape of the fan(s). Adequate
air volume must be obtained and this will require appropriately sized vents. Intake vents should be
located in front of the intake fan(s) and adjacent to the drive bays. Venting should be
approximately 50% to 60% open in the EMI containment area due to EMI constraints. Outside the
EMI containment area, the open percentage can be greater if needed for aesthetic appeal (i.e.,
bezel/cosmetics). For more information concerning EMI constraints and Pentium II processor
based system design, see the Pentium II Processor EMI Design Guidelines Application Note.
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