MPC8264AVR datasheet(11/48 Pages) MOTOROLA

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MOTOROLA

MPC826xA (HiP4) Family Hardware Speciﬁcations

Electrical and Thermal Characteristics

1.2.2

Thermal Characteristics

Table 4 describes thermal characteristics.

1.2.3

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)

where K is a constant pertaining to the particular part. K can be determined from equation (3) by measuring

PD (at equilibrium) for a known TA. Using this value of K, the values of PD and TJ can be obtained by solving

equations (1) and (2) iteratively for any value of TA.

Table 4. Thermal Characteristics for 480 TBGA Package

Characteristics

Symbol

Value

Unit

Air Flow

Junction to ambient

θJA

131

1 Assumes a single layer board with no thermal vias

°C/W

NC2

2 Natural convection

101

1 m/s

113

3 Assumes a four layer board

1 m/s

Junction to board4

4 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 case5

5 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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