DSP56F826 Motorola, DSP56F826 Datasheet - Page 41

• Manufacturer Part Number: DSP56F826
• Description: 16-bit Digital Signal Processor
• Manufacturer: Motorola

Part 5 Design Considerations
5.1 Thermal Design Considerations
An estimation of the chip junction temperature, T
Where:
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
change the case-to-ambient thermal resistance, R
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 R
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:
JC
•
•
is device-related and cannot be influenced by the user. The user controls the thermal environment to
T
R
P
R
R
R
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.
A
D
Equation 1:
Equation 2:
JA
JA
JC
CA
= ambient temperature °C
= power dissipation in package
= package junction-to-case thermal resistance °C/W
= package junction-to-ambient thermal resistance °C/W
= package junction-to-ambient thermal resistance °C/W
= package case-to-ambient thermal resistance °C/W
T
R
J
JA
=
T
=
A
DSP56F826 Preliminary Technical Data
R
+
JC
P
D
+
R
R
CA
JA
J
CA
, in C can be obtained from the equation:
. For example, the user can change the air flow around
JA
do not satisfactorily answer whether the
Thermal Design Considerations
41