GS-R51212S datasheet(8/8 Pages) STMICROELECTRONICS

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The dissipated power in this operating condition is

about 7.4W (at typical efficiency of 81%), and the

case temperature of the module will be:

Tcase

= Tamb + Pd × Rth = 40 + 7.4 × 7.5 = 95.5

°C

This value exceeds the maximum allowed tempera-

ture and an external heat-sink must be added. To

this purpose four holes (see mechanical drawing)

are provided on the metal surface of the module.

To calculate this heat-sink, let’s first determine what

the total thermal resistance should be:

Rth

= Tcase(max) − Tamb

= 85 − 40

7.4

= 5.40

°C ⁄ W

This value is the resulting value of the parallel

connection of GS-R thermal resistance and of the

additional heatsink thermal resistance.

Rth

(GSR)

× Rth (Heatsink)

Rth

(GSR

) + Rth (Heatsink)

= 5.40°C/ W

To calculate the thermal resistance of the additional

heat-sink the following equation may be used:

Rth

(Heatsink)= 5.40 × Rth (GSR)

Rth(GSR) − 5,40

= 5.40× 7.5

7.5

− 5.40

= 19.3 °C/ W

In instead of or in addition to the external heatsink,

a forced ventilation with an air speed of about 200

linear feet/minute can be used reducing the thermal

resistance of the module at the specified value.

Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the

consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No

license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specification mentioned

in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.

SGS-THOMSON Microelectronics products are not authorized for use as critical components in life support devices or systems without express

written approval of SGS-THOMSON Microelectronics.

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GS-R51212S/GS-R51515S

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