DSP56364D Motorola Inc, DSP56364D Datasheet - Page 91

• Manufacturer Part Number: DSP56364D
• Description: 24-Bit Audio Digital Signal Processor
• Manufacturer: Motorola Inc

4.1
An estimation of the chip junction temperature, T
Historically, thermal resistance has been expressed as the sum of a junction-to-case thermal resistance
and a case-to-ambient thermal resistance.
R
change the case-to-ambient thermal resistance, R
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
the thermal performance is adequate, a system level model may be appropriate.
A complicating factor is the existence of three common ways for determining the junction-to-case thermal
resistance in plastic packages.
MOTOROLA
JC
•
•
•
is device-related and cannot be influenced by the user. The user controls the thermal environment to
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
resistance is computed using the value obtained by the equation
(T
THERMAL DESIGN CONSIDERATIONS
J
– T
Where:
Where:
T
T J
R JA
)/P
=
D
.
T A
=
R JC
+
R
R
R
R
qJA
P
P D
T
CA
Freescale Semiconductor, Inc.
JC
JA
D
A
For More Information On This Product,
+
= ambient temperature C
= package junction-to-ambient thermal resistance C/W
= power dissipation in package W
= package junction-to-ambient thermal resistance °C/W
= package junction-to-case thermal resistance °C/W
= package case-to-ambient thermal resistance °C/W
R CA
R JA
DSP56364 Advance Information
Go to: www.freescale.com
J
, in C can be obtained from the following equation:
T
) is determined by a thermocouple, the thermal
CA
DESIGN CONSIDERATIONS
. For example, the user can change the air flow
JA
do not satisfactorily answer whether
SECTION 4
4-1