4-2
DSP56367
MOTOROLA
Design Considerations
Thermal Design Considerations
A complicating factor is the existence of three common ways for determining the
junction-to-case thermal resistance in plastic packages.
•
To minimize temperature variation across the surface, the thermal resistance is
measured 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.
•
To define a value approximately equal to a junction-to-board thermal resistance, the
thermal resistance is measured from the junction to where the leads are attached to the
case.
•
If the temperature of the package case (T
T
) is determined by a thermocouple, the
thermal resistance is computed using the value obtained by the equation
(T
J
– T
T
)/P
D
.
As noted above, the junction-to-case thermal resistances quoted in this data sheet are
determined using the first definition. From a practical standpoint, that value is also suitable for
determining the junction temperature from a case thermocouple reading in forced convection
environments. In natural convection, using the junction-to-case thermal resistance to estimate
junction temperature from a thermocouple reading on the case of the package will estimate a
junction temperature slightly hotter than actual temperature. Hence, the new thermal metric,
thermal characterization parameter or
Ψ
JT
, has been defined to be (T
J
– T
T
)/P
D
. This value
gives a better estimate of the junction temperature in natural convection when using the
surface temperature of the package. Remember that surface temperature readings of packages
are subject to significant errors caused by inadequate attachment of the sensor to the surface
and to errors caused by heat loss to the sensor. The recommended technique is to attach a
40-gauge thermocouple wire and bead to the top center of the package with thermally
conductive epoxy.
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: ......