MOTOROLA
DSP56367
4-1
SECTION 4
DESIGN CONSIDERATIONS
4.1
THERMAL DESIGN CONSIDERATIONS
An estimation of the chip junction temperature, T
J
, in
°
C can be obtained from the following
equation:
Where:
T
A
= ambient temperature
°
C
R
qJA
= package junction-to-ambient thermal resistance
°
C/W
P
D
= power dissipation in package W
Historically, thermal resistance has been expressed as the sum of a junction-to-case thermal
resistance and a case-to-ambient thermal resistance.
Where:
R
θ
JA
= package junction-to-ambient thermal resistance °C/W
R
θ
JC
= package junction-to-case thermal resistance °C/W
R
θ
CA
= package case-to-ambient thermal resistance °C/W
R
θ
JC
is device-related and cannot be influenced by the user. The user controls the thermal
environment to change the case-to-ambient thermal resistance, R
θ
CA
. 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% 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 R
θ
JA
do not
satisfactorily answer whether the thermal performance is adequate, a system level model may
be appropriate.
T
J
T
A
P
D
R
θ
JA
×
(
)
+
=
R
θ
JA
R
θ
JC
R
θ
CA
+
=
Summary of Contents for DSP56367
Page 16: ...xvi MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 22: ...xxii MOTOROLA List of Figures Figure Number Title Page Number ...
Page 26: ...xxvi MOTOROLA List of Tables Table Number Title Page Number ...
Page 148: ...4 6 DSP56367 MOTOROLA Design Considerations PLL Performance Issues ...
Page 248: ...9 30 DSP56367 MOTOROLA Serial Host Interface SHI Programming Considerations ...
Page 306: ...10 58 DSP56367 MOTOROLA Enhanced Serial Audio Interface ESAI ESAI Initialization Examples ...
Page 389: ...Bootstrap ROM Contents MOTOROLA DSP56367 A 15 end ...
Page 390: ...A 16 DSP56367 MOTOROLA Bootstrap ROM Contents ...
Page 432: ...C 8 DSP56367 MOTOROLA JTAG BSDL ...
Page 484: ...D 52 DSP56367 MOTOROLA Programmer s Reference ...
Page 490: ...E 6 DSP56367 MOTOROLA Power Consumption Benchmark ...
Page 516: ...F 26 DSP56367 MOTOROLA IBIS Model ...
Page 522: ...Index 6 MOTOROLA Index ...
Page 523: ......