DSP56800FM Просмотр технического описания (PDF) - Motorola => Freescale

Номер в каталоге

Компоненты Описание

производитель

DSP56800FM

16-bit Hybrid Controller

Motorola => Freescale 

Freescale Semiconductor, Inc.

Thermal Design Considerations

Part 5 Design Considerations

5.1 Thermal Design Considerations

An estimation of the chip junction temperature, TJ, in °C can be obtained from the equation:

Equation 1: TJ = TA + (PD × RθJA)

Where:

TA = ambient temperature °C

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

PD = 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:

Equation 2: RθJA = RθJC + RθCA

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 the PCB. This

model is most useful for ceramic packages with heat sinks; some 90% 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 estimations obtained from RθJA do not satisfactorily answer whether the

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

Definitions:

A complicating factor is the existence of three common definitions for determining the junction-to-case

thermal resistance in plastic packages:

• Measure the thermal resistance from the junction to the outside surface of the package (case) closest

to the chip mounting area when that surface has a proper heat sink. This is done to minimize

temperature variation across the surface.

• Measure the thermal resistance from the junction to where the leads are attached to the case. This

definition is approximately equal to a junction-to-board thermal resistance.

56F826 Technical Data

45

For More Information On This Product,

Go to: www.freescale.com

Share Link: