MPC8250 datasheet(10/62 Pages) FREESCALE

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MPC8250 Hardware Specifications, Rev. 2

Freescale Semiconductor

Electrical and Thermal Characteristics

2.2

Thermal Characteristics

Table 4 describes thermal characteristics.

2.3

Power Considerations

The average chip-junction temperature, TJ, in °C can be obtained from the following:

TJ = TA + (PD x θJA)

(1)

where

TA = ambient temperature °C

JA = package thermal resistance, junction to ambient, °C/W

PD = PINT + PI/O

PINT = IDD x VDD Watts (chip internal power)

PI/O = power dissipation on input and output pins (determined by user)

For most applications PI/O < 0.3 x PINT. If PI/O is neglected, an approximate relationship between PD and

TJ is the following:

PD = K/(TJ + 273° C)

(2)

Solving equations (1) and (2) for K gives:

K = PD x (TA + 273° C) + θJA x PD

(3)

The default configuration of the CPM pins (PA[0–31], PB[4–31], PC[0–31], PD[4–31]) is input. To prevent excessive

DC current, it is recommended to either pull unused pins to GND or VDDH, or to configure them as outputs.

The leakage current is measured for nominal VDD, VCCSYN, and VDD.

Table 4. Thermal Characteristics

Characteristic

Symbol

Value

Unit

Air Flow

480 TBGA

516 PBGA

Junction to ambient—

single-layer board 1

Assumes no thermal vias

θJA

°C/W

Natural convection

1 m/s

Junction to ambient—

four-layer board

Natural convection

813

1 m/s

Junction to board 2

Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is

measured on the top surface of the board near the package.

θJB

°C/W

—

Junction to case 3

Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883

Method 1012.1).

θJC

1.1

°C/W

—

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