ST7293 datasheet(40/69 Pages) STMICROELECTRONICS

40 / 69 page

40/69

ST7294

6.2 POWER CONSIDERATIONS

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 ICC and VCC, expressed in

Watts. This is the Chip’s Internal Power Dissipa-

tion.

–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

configured 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 xPD

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 val-

ue of TA.

Table 11. Thermal Characteristics

Symbol

Characteristics

Value

Unit

θJA

Thermal Resistance

PDIP28

PSO28

°C/W

ST7293 数据表(PDF) 40 Page - STMicroelectronics

ST7293 数据表(HTML) 40 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69

数据表下载