DSP56321RMSLASHD datasheet(67/88 Pages) NXP

67 / 88 page

4-1

Chapter 4

Design

Considerations

4.1 Thermal Design Considerations

An estimate of the chip junction temperature, TJ, in °C can be obtained from

this equation:

Equation 1:

Where:

ambient temperature °C

RθJA

package junction-to-ambient thermal resistance °C/W

power dissipation in package

Historically, thermal resistance has been expressed as the sum of a

junction-to-case thermal resistance and a case-to-ambient thermal resistance,

as in this equation:

Equation 2:

Where:

RθJA

package junction-to-ambient thermal resistance °C/W

RθJC

package junction-to-case thermal resistance °C/W

RθCA

package case-to-ambient thermal resistance °C/W

RθJC is device-related and cannot be influenced by the user. The user controls

the thermal environment to change the case-to-ambient thermal resistance,

RθCA. For example, the user can change the air flow around the device, add a

heat sink, change the mounting arrangement on the printed circuit board

(PCB) or otherwise change the thermal dissipation capability of the area

surrounding the device on a PCB. This model is most useful for ceramic

packages with heat sinks; some 90 percent of the heat flow is dissipated

through the case to the heat sink and out to the ambient environment. For

ceramic packages, in situations where the heat flow is split between a path to

the case and an alternate path through the PCB, analysis of the device thermal

performance may need the additional modeling capability of a system-level

thermal simulation tool.

The thermal performance of plastic packages is more dependent on the

temperature of the PCB to which the package is mounted. Again, if the

estimates obtained from RθJA do not satisfactorily answer whether the thermal

performance is adequate, a system-level model may be appropriate.

RθJA

()

RθJA

RθJC RθCA

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

DSP56321RM/D Datasheet(PDF) 67 Page - NXP Semiconductors

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