ST10F276 datasheet(177/229 Pages) STMICROELECTRONICS

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ST10F276

Electrical characteristics

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23.3

Power considerations

The average chip-junction temperature, TJ, in degrees Celsius, is 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 Watt. This is the Chip Internal Power,

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

Most often in applications, PI/O< PINT ,which may be ignored. On the other hand, PI/O may

be significant if the device is configured to continuously drive 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

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

Based on thermal characteristics of the package and with reference to the power

consumption figures provided in the next tables and diagrams, the following product

classification can be proposed. In any case, the exact power consumption of the device

inside the application must be computed according to different working conditions, thermal

profiles, real thermal resistance of the system (including printed circuit board or other

substrata) and I/O activity.

For details on operating conditions concerning the usage of A/D converter, refer to Section 23.7.

Table 88.

Thermal characteristics

Symbol

Description

Value (typical)

Unit

ΘJA

Thermal resistance junction-ambient

PQFP 144 - 28 x 28 x 3.4 mm / 0.65 mm pitch

LQFP 144 - 20 x 20 mm / 0.5 mm pitch

LQFP 144 - 20 x 20 mm / 0.5 mm pitch on four layer

FR4 board (2 layers signals / 2 layers power)

°C/W

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