Environmental Data
CAUTION: Tables 3–2 through 3–7 present the maximum ambient temperature
for the DECchip 21066. Other limitations on ambient operating
temperature may apply, including storage devices, power supplies,
PCI or ISA option modules, or other chips on the MLB.
The three recommended DECchip 21066 heatsinks are made from 6061–T6
aluminum with clear anodized finish:
•
Low profile (2.20 inches L x 2.20 inches W x 0.34 inches H)
•
High profile (2.27 inches L x 2.27 inches W x 0.90 inches H)
•
Integral fan/heatsink (2.20 inches L x 2.20 inches W x 0.42 inches H)
The third heatsink uses an attached fan. Dimensions for the fan are 2.36
inches L x 2.36 inches W x 0.59 inches H. The fan delivers 14 CFM at 12
Vdc and 90 mA.
3.1.2.1
DECchip 21066 (166 MHz) Cooling Requirements
Tables 3–2 through 3–4 list the DECchip 21066 (166 MHz) cooling
requirements using a low-profile heatsink, high-profile heatsink, and
fan/heatsink, respectively.
Table 3–2
DECchip 21066 (166 MHz) Cooling Using Low-Profile Heatsink
Air
Velocity
LFM
AXPpci 33
CPU Power
T c
Max
Theta jc
Theta ja
Theta ca
Maximum
Ambient
Temperature Notes
400
21 W
85°C
0.70°C/W
3.80°C/W
3.10°C/W
20°C
1
600
21 W
85°C
0.70°C/W
2.80°C/W
2.10°C/W
41°C
1
800
21 W
85°C
0.70°C/W
2.35°C/W
1.65°C/W
50°C
1, 2
1,000
21 W
85°C
0.70°C/W
2.10°C/W
1.40°C/W
56°C
1, 2
Using part number 12–35739–18 low-profile heatsink.
Notes:
1 If the recommended thermal pad (thermal interface between the 21066 and heatsink) is not used, the Theta jc
and Theta ja values will increase by 0.45°C/W. The end result is a decrease in maximum allowable ambient
temperature by 9.5°C.
2 Operation above 40°C ambient temperature requires further thermal analysis by the system integrator. This
ensures that maximum operating temperatures are not exceeded for any other device including storage devices,
power supplies, PCI or ISA option modules, or other chips on the MLB.
3–2
Summary of Contents for AXPpci 33
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Page 22: ...Physical Description Figure 2 2 MLB Mechanical Drawing MR 6414 AI 2 4...
Page 23: ...Physical Description Figure 2 3 MLB Component Outline Drawing MR 6401 AI 2 5...
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