MPC852TVR66 Freescale Semiconductor, MPC852TVR66 Datasheet - Page 9

• Manufacturer Part Number: MPC852TVR66
• Description: IC MPU POWERQUICC 66MHZ 256-PBGA
• Manufacturer: Freescale Semiconductor

Specifications of MPC852TVR66

• Processor Type: MPC8xx PowerQUICC 32-Bit
• Speed: 66MHz
• Voltage: 1.8V
• Mounting Type: Surface Mount
• Package / Case: 256-PBGA
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -

The junction-to-ambient thermal resistance is an industry standard value that provides a quick and easy estimation
of thermal performance. However, the answer is only an estimate; test cases have demonstrated that errors of a factor
of two (in the quantity T
7.2 Estimation with Junction-to-Case Thermal Resistance
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:
R
where:
R
case-to-ambient thermal resistance, R
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 Estimation with Junction-to-Board Thermal Resistance
A simple package thermal model that 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. Thermal performance of most plastic packages and especially PBGA packages is strongly
dependent on the board temperature. If the board temperature is known, an estimate of the junction temperature in
the environment can be made using the following equation:
T
where:
If the board temperature is known and the heat loss from the package case to the air can be ignored, acceptable
predictions of junction temperature can be made. For this method to work, the board and board mounting must be
similar to the test board used to determine the junction-to-board thermal resistance, namely a 2s2p (board with a
power and a ground plane) and vias attaching the thermal balls to the ground plane.
7.4 Estimation Using Simulation
When the board temperature is not known, a thermal simulation of the application is needed. The simple two-resistor
model can be used with the thermal simulation of the application [2], or a more accurate and complex model of the
package can be used in the thermal simulation.
Freescale Semiconductor
J
θJA
θJC
= T
is device-related and cannot be influenced by the user. The user adjusts the thermal environment to affect the
= R
B
R
R
R
R
T
P
+(R
θJC
D
B
θJA
θJC
θCA
θJB
= board temperature ºC
= power dissipation in package
θJB
+ R
= junction-to-case thermal resistance (ºC/W)
= junction-to-board thermal resistance (ºC/W)
= junction-to-ambient thermal resistance (ºC/W)
= case-to-ambient thermal resistance (ºC/W)
x P
θCA
D
)
J
-T
A
) are possible.
MPC852T Hardware Specifications, Rev. 3.1
θCA
. For instance, the user can change the air flow around the device, add a
Thermal Calculation and Measurement
9