MPC7457 datasheet(63/71 Pages) FREESCALE

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System Design Information

MPC7457 RISC Microprocessor Hardware Specifications, Rev. 8

Freescale Semiconductor

The Bergquist Company

800-347-4572

18930 West 78th St.

Chanhassen, MN 55317

Internet: www.bergquistcompany.com

Chomerics, Inc.

781-935-4850

77 Dragon Ct.

Woburn, MA 01888-4014

Internet: www.chomerics.com

Dow-Corning Corporation

800-248-2481

Dow-Corning Electronic Materials

2200 W. Salzburg Rd.

Midland, MI 48686-0997

Internet: www.dow.com

Shin-Etsu MicroSi, Inc.

888-642-7674

10028 S. 51st St.

Phoenix, AZ 85044

Internet: www.microsi.com

Thermagon Inc.

888-246-9050

4707 Detroit Ave.

Cleveland, OH 44102

Internet: www.thermagon.com

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:

Tj = TI + Tr + (RθJC + Rθint + Rθsa) × Pd

where:

Tj is the die-junction temperature

TI is the inlet cabinet ambient temperature

Tr is the air temperature rise within the computer cabinet

RθJC is the junction-to-case thermal resistance

Rθint is the adhesive or interface material thermal resistance

Rθsa is the heat sink base-to-ambient thermal resistance

Pd is the power dissipated by the device

During operation, the die-junction temperatures (Tj) 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 (Ta)

may range from 30° to 40°C. The air temperature rise within a cabinet (Tr) may be in the range of 5° to

10°C. The thermal resistance of the thermal interface material (Rθint) is typically about 1.5°C/W. For

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