CS5257A−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

current regulator such as the CS5257A−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 our

application note “Thermal Management,” document

number AND8036/D, available through the Literature

Distribution

Center

or

via

our

website

at

http://www.onsemi.com.