ST7263 datasheet(94/109 Pages) STMICROELECTRONICS

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ST7263

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7.2 THERMAL CHARACTERISTICS

The average chip-junction temperature, TJ, in de-

grees Celsius, may be calculated using the follow-

ing equation:

TJ = TA + (PD x θJA) (1)*

Where:

– TA is the Ambient Temperature in °C,

–

θJ

A is the Package Junction-to-Ambient Thermal

Resistance, in

°C/W,

– PD is the sum of PINT and 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; User Determined.

For most applications PI/O<PINT and may be ne-

glected. PI/O may be significant if the device is con-

figured to drive Darlington bases or sink LED Loads.

An approximate relationship between PD and TJ

(if PI/O is neglected) is given by:

PD = K÷ (TJ + 273°C) (2)

Therefore:

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 val-

ue of K, the values of PD and TJ may be obtained

by solving equations (1) and (2) iteratively for any

value of TA.

Table 25. Thermal Characteristics

(*): Maximum chip dissipation can directly be obtained from Tj (max), θJA and TA parameters.

Symbol

Package

Typical Value

Unit

θJ

SO34

°C/W

PSDIP32

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