Design Considerations; Section 4 Design Considerations - Motorola NXP SYMPHONY DSP56007 Technical Data Manual

Freescale Semiconductor, Inc.

DESIGN CONSIDERATIONS

THERMAL DESIGN CONSIDERATIONS
An estimation of the chip junction temperature, T
equation:
Equation 1:
T
Where:
T = ambient temperature ˚C
A
R = package junction-to-ambient thermal resistance ˚C/W
θJA
P = power dissipation in package
D
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:
R
Where:
R = package junction-to-ambient thermal resistance ˚C/W
θJA
R = package junction-to-case thermal resistance ˚C/W
θJC
R = package case-to-ambient thermal resistance ˚C/W
θCA
R is device-related and cannot be influenced by the user. The user controls the
θJC
thermal environment to change the case-to-ambient thermal resistance, R
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% 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.
MOTOROLA
SECTION
( × )
= T + P R
θJA
J A D
= R + R
θJA θJC θCA
DSP56007/D
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4
, in °C can be obtained from the
J
θCA
. For
4-1