MPC862 MOTOROLA [Motorola, Inc], MPC862 Datasheet - Page 13

• Manufacturer Part Number: MPC862
• Description: Hardware Specifications
• Manufacturer: MOTOROLA [Motorola, Inc]

7.2
Historically, the thermal resistance has frequently been expressed as the sum of a junction-to-case thermal
resistance and a case-to-ambient thermal resistance:
where:
R
affect the case-to-ambient thermal resistance, R
the device, add a heat sink, change the mounting arrangement on the printed circuit board, or change the
thermal dissipation on the printed circuit board surrounding the device. This thermal model is most useful
for ceramic packages with heat sinks where some 90% of the heat flows through the case and the heat sink
to the ambient environment. For most packages, a better model is required.
7.3
A simple package thermal model which has demonstrated reasonable accuracy (about 20%) is a two resistor
model consisting of a junction-to-board and a junction-to-case thermal resistance. The junction-to-case
covers the situation where a heat sink is used or where a substantial amount of heat is dissipated from the
top of the package. The junction-to-board thermal resistance describes the thermal performance when most
of the heat is conducted to the printed circuit board. It has been observed that the thermal performance of
most plastic packages and especially PBGA packages is strongly dependent on the board temperature; see
Figure 3.
MOTOROLA
θJC
is device related and cannot be influenced by the user. The user adjusts the thermal environment to
R
R
R
θJA
θJC
θCA
Estimation with Junction-to-Case Thermal Resistance
R
Estimation with Junction-to-Board Thermal Resistance
= junction-to-ambient thermal resistance (ºC/W)
= junction-to-case thermal resistance (ºC/W)
θJA
= case-to-ambient thermal resistance (ºC/W)
= R
1 0 0
Figure 3. Effect of Board Temperature Rise on Thermal Behavior
9 0
8 0
7 0
6 0
5 0
4 0
3 0
2 0
1 0
0
θJC
0
+ R
Board Temperture Rise Above Ambient Divided by Package
MPC862/857T/857DSL Hardware Specifications
Freescale Semiconductor, Inc.
θCA
For More Information On This Product,
2 0
Go to: www.freescale.com
θCA
. For instance, the user can change the air flow around
Power
4 0
Thermal Calculation and Measurement
6 0
8 0
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