STRT71XF datasheet(69/74 Pages) STMICROELECTRONICS

69 / 74 page

STR71xF

Package characteristics

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3.2

Thermal characteristics

The average chip-junction temperature, TJ, in degrees Celsius, may be calculated using the

following equation:

TJ = TA + (PD x ΘJA)

(1)

Where:

●

TA is the Ambient Temperature in °C,

●

ΘJA is the Package Junction-to-Ambient Thermal Resistance, in °C/W,

●

PD is the sum of PINT and PI/O (PD = PINT + PI/O),

●

PINT is the product of IDD and VDD, expressed in Watts. This is the Chip Internal Power.

PI/O represents the Power Dissipation on Input and Output Pins;

Most of the time for the application PI/O< PINT and can be neglected. On the other hand, PI/O

may be significant if the device is configured to drive continuously external modules and/or

memories.

An approximate relationship between PD and TJ (if PI/O is neglected) is given by:

PD = K / (TJ + 273°C)

(2)

Therefore (solving equations 1 and 2):

K = PD x (TA + 273°C) + ΘJA x PD

(3)

where:

K is a constant for the particular part, which may 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

may be obtained by solving equations (1) and (2) iteratively for any value of TA.

Table 38.

Thermal characteristics

Symbol

Parameter

Value

Unit

ΘJA

Thermal Resistance Junction-Ambient

LQFP 144 - 20 x 20 mm / 0.5 mm pitch

°C/W

ΘJA

Thermal Resistance Junction-Ambient

LQFP 64 - 10 x 10 mm / 0.5 mm pitch

°C/W

ΘJA

Thermal Resistance Junction-Ambient

LFBGA 64 - 8 x 8 x 1.7mm

°C/W

ΘJA

Thermal Resistance Junction-Ambient

LFBGA 144 - 10 x 10 x 1.7mm

°C/W

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