CS8122
Application Notes: continued
Heat Sinks
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 will have a thermal resistance. Like
series electrical resistances, these resistances are summed
to determine the value of R
QJA
:
R
QJA
= R
QJC
+ R
QCS
+ R
QSA
(3)
where:
R
QJC
= the junctionÐtoÐcase thermal resistance,
R
QCS
= the caseÐtoÐheatsink thermal resistance, and
R
QSA
= the heatsinkÐtoÐambient thermal resistance.
R
QJC
appears in the package section of the data sheet. Like
R
QJA
, it too is a function of package type. R
QCS
and R
QSA
are functions of the package type, heatsink and the inter-
face between them. These values appear in heat sink data
sheets of heat sink manufacturers.
7
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
