STR910FAM32X6 datasheet(95/99 Pages) STMICROELECTRONICS

95 / 99 page

STR91xFAx32 STR91xFAx42 STR91xFAx44

Package mechanical data

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9.2

Thermal characteristics

The average chip-junction temperature, TJ must never exceed 125° C.

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 applications PI/O< PINT and may be neglected. On the other hand,

PI/O may be significant if the device is configured to drive continuously external modules

and/or memories. The worst case PINT of the STR91xFA is 500mW (IDD x VDD, or 250mA x

2.0V).

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

2(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 49.

Thermal characteristics

Symbol

Parameter

Value

Unit

ΘJA

Thermal Resistance Junction-Ambient

LQFP 80 - 12 x 12 mm / 0.5 mm pitch

41.5

°C/W

ΘJA

Thermal Resistance Junction-Ambient

LQFP128 - 14 x 14 mm / 0.4 mm pitch

°C/W

ΘJA

Thermal Resistance Junction-Ambient

LFBGA 144 - 10 x 10 x 1.7mm

36.5

°C/W

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