CS5258−1

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9

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 which is measured in degrees per watt. Like series

electrical resistances, these thermal resistances are summed

to determine the total thermal resistance between the die

resistance is comprised of three components. These resistive

equation is:

RQJA + RQJC ) RQCS ) RQSA

TO−220 package. For a high current regulator such as the

CS5258−1 the majority of heat is generated in the power

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

the proper heat sink selected. For further discussion on heat

sink selection, see our application note “Thermal

Management,” document number AND8036/D, available

through the Literature Distribution Center or via our website

at http://www.onsemi.com.