CS5207A−1

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7

The maximum ambient temperature and the power

dissipation are determined by the design while the

maximum junction temperature and the thermal resistance

depend on the manufacturer and the package type. The

maximum power dissipation for a regulator is:

PD(max) + (VIN(max) * VOUT(min))IOUT(max) ) VIN(max)

IIN(max)

A heat sink effectively increases the surface area of the

package to improve the flow of heat away from the IC and

into the surrounding air. Each material in the heat flow path

between the IC and the outside environment has a thermal

resistance. Like series electrical resistances, these

resistances are summed to determine the total thermal

resistance between the die junction and the surrounding air,

components. These resistive terms are measured from

RQJA + RQJC ) RQCS ) RQSA

current regulator such as the CS5207A−1 the majority of

heat is generated in the power transistor section. The value

depends on factors such as package type, heat sink interface

(is an insulator and thermal grease used?), and the contact

area between the heat sink and the package. Once these

calculations are complete, the maximum permissible value

For further discussion on heat sink selection, see application

note

“Thermal

Management,”

document

number

AND8036/D, available through the Literature Distribution

Center or via our website at http://onsemi.com.