ST10F271 datasheet(125/173 Pages) STMICROELECTRONICS

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ST10F271

Electrical characteristics

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24.3

Power considerations

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,

JA 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 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.

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.

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

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

classification can be proposed. Anyhow, 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), I/O

activity, and so on.

The value of the VSTBY voltage is specified in the range 4.5 - 5.5 Volt. Nevertheless, it is acceptable to exceed the upper

limit (up to 6.0 Volt) for a maximum of 100 hours over the global 300000 hours, representing the lifetime of the device

(about 30 years). On the other hand, it is possible to exceed the lower limit (down to 4.0 Volt) whenever RTC and 32kHz

on-chip oscillator amplifier are turned off (only Stand-by RAM powered through VSTBY pin in Stand-by mode). When

VSTBY voltage is lower than main VDD, the input section of VSTBY/EA pin can generate a spurious static consumption on

VDD power supply (in the range of tenth of

µA).

For details on operating conditions concerning the usage of A/D Converter refer to Section 24.7.

Table 61.

Thermal characteristics

Symbol

Description

Value (typical)

Unit

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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