MC7457RX1267LC Datasheet, PDF (63/71 Pages) Freescale Semiconductor, Inc – Microprocessor

System Design Information
The Bergquist Company
18930 West 78^th St.
Chanhassen, MN 55317
Internet: www.bergquistcompany.com
800-347-4572
Chomerics, Inc.
77 Dragon Ct.
Woburn, MA 01888-4014
Internet: www.chomerics.com
781-935-4850
Dow-Corning Corporation
Dow-Corning Electronic Materials
2200 W. Salzburg Rd.
Midland, MI 48686-0997
Internet: www.dow.com
800-248-2481
Shin-Etsu MicroSi, Inc.
10028 S. 51st St.
Phoenix, AZ 85044
Internet: www.microsi.com
888-642-7674
Thermagon Inc.
4707 Detroit Ave.
Cleveland, OH 44102
Internet: www.thermagon.com
888-246-9050
The following section provides a heat sink selection example using one of the commercially available heat
sinks.
9.8.3 Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as follows:
T_j = T_I + T_r + (R_θJC + R_θint + R_θsa) × P_d
where:
T_j is the die-junction temperature
T_I is the inlet cabinet ambient temperature
T_r is the air temperature rise within the computer cabinet
R_θJC is the junction-to-case thermal resistance
R_θint is the adhesive or interface material thermal resistance
R_θsa is the heat sink base-to-ambient thermal resistance
P_d is the power dissipated by the device
During operation, the die-junction temperatures (T_j) should be maintained less than the value specified in
Table 4. The temperature of air cooling the component greatly depends on the ambient inlet air temperature
and the air temperature rise within the electronic 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 thermal interface material (R_θint) is typically about 1.5°C/W. For
MPC7457 RISC Microprocessor Hardware Specifications, Rev. 8
Freescale Semiconductor
63