5/20/99
Version 1.51
PowerPC 740 and PowerPC 750 Datasheet
Page 43
PowerPC 740 and PowerPC 750 Embedded Microprocessor
IBM CMOS 0.20 um Copper Technology EMPPC740L and EMPPC750L
Chomerics, Inc.
617-935-4850
77 Dragon Court
Woburn, MA 01888-4850
Thermagon, Inc.
216-741-7659
3256 West 25th Street
Cleveland, OH 44109-1668
Loctite Corporation
860-571-5100
1001 Trout Brook Crossing
Rocky Hill, CT 06067
AI Technology (e.g. EG7655)
609-882-2332
1425 Lower Ferry Road
Trent, NJ 08618
The following section provides a heat sink selection example using one of the commercially available heat
sinks.
Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as follows.
T
J = TA + TR + (
θ
JC +
θ
INT +
θ
SA)
× P
D
Where:
T
J is the die-junction temperature
T
A is the inlet cabinet ambient temperature
T
R is the air temperature rise within the system cabinet
θ
JC is the junction-to-case thermal resistance
θ
INT is the thermal resistance of the thermal interface material
θ
SA is the heat sink-to-ambient thermal resistance
P
D is the power dissipated by the device
Typical die-junction temperatures (T
J) should be maintained less than the value specified in Table “Package upon the ambient inlet air temperature and the air temperature rise within the computer cabinet. An electronic
cabinet inlet-air temperature (T
A) may range from 30 to 40
°C. The air temperature rise within a cabinet (T
R)
may be in the range of 5 to 10
°C. The thermal resistance of the interface material (θ
INT) is typically about 1
°C/
W. Assuming a T
A of 30
°C, a T
R of 5
°C, a CBGA package θ
JC = 0.03, and a power dissipation (PD) of 5.0 watts,
the following expression for T
J is obtained.
Die-junction temperature: T
J = 30
°C + 5°C + (0.03°C/W +1.0°C/W + θ
SA)
× 5W
For a Thermalloy heat sink #2328B, the heat sink-to-ambient thermal resistance (
θ
SA) versus air flow velocity