MPC5200VR400B 查看數據表（PDF） - Freescale Semiconductor

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MPC5200VR400B

SDRAM/DDR Memory Controller

Freescale Semiconductor 

RθJA = RθJC+RθCA

Eqn. 4

where:

RθJA = junction to ambient thermal resistance (ºC/W)

RθJC = junction to case thermal resistance (ºC/W)

RθCA = case to ambient thermal resistance (ºC/W)

RθJC is device related and cannot be influenced by the user. The user controls the thermal environment to change the case to

ambient thermal resistance, RθCA. For instance, the user can change the air flow around the device, add a heat sink, change the

mounting arrangement on printed circuit board, or change the thermal dissipation on the printed circuit board surrounding the

device. This description is most useful for ceramic packages with heat sinks where some 90% of the heat flow is through the

case to the heat sink to ambient. For most packages, a better model is required.

A more accurate thermal model can be constructed from the junction to board thermal resistance and the junction to case thermal

resistance. The junction to case covers the situation where a heat sink is used or 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. This model can be used for hand estimations or for a computational fluid dynamics (CFD)

thermal model.

To determine the junction temperature of the device in the application after prototypes are available, the Thermal

Characterization Parameter (ΨJT) can be used to determine the junction temperature with a measurement of the temperature at

the top center of the package case using the following equation:

TJ = TT+(ΨJT × PD)

Eqn. 5

where:

TT = thermocouple temperature on top of package (ºC)

ΨJT = thermal characterization parameter (ºC/W)

PD = power dissipation in package (W)

The thermal characterization parameter is measured per JESD51-2 specification using a 40-gauge type T thermocouple epoxied

to the top center of the package case. The thermocouple should be positioned, so that the thermocouple junction rests on the

package. A small amount of epoxy is placed over the thermocouple junction and over approximately one mm of wire extending

from the junction. The thermocouple wire is placed flat against the package case to avoid measurement errors caused by cooling

effects of the thermocouple wire.

1.2 Oscillator and PLL Electrical Characteristics

The MPC5200B System requires a system-level clock input SYS_XTAL. This clock input may be driven directly from an

external oscillator or with a crystal using the internal oscillator.

There is a separate oscillator for the independent Real-Time Clock (RTC) system.

The MPC5200B clock generation uses two phase locked loop (PLL) blocks.

• The system PLL (SYS_PLL) takes an external reference frequency and generates the internal system clock. The

system clock frequency is determined by the external reference frequency and the settings of the SYS_PLL

configuration.

• The e300 core PLL (CORE_PLL) generates a master clock for all of the CPU circuitry. The e300 core clock frequency

is determined by the system clock frequency and the settings of the CORE_PLL configuration.

MPC5200B Data Sheet, Rev. 4

10

Freescale Semiconductor

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