Application Notes: continued
where:
Heat Sinks
R
R
R
QJC = the junctionÐtoÐcase thermal resistance,
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.
QCS = the caseÐtoÐheatsink thermal resistance, and
QSA = the heatsinkÐtoÐambient thermal resistance.
R
R
QJC appears in the package section of the data sheet. Like
QJA, it too is a function of package type. RQCS and RQSA
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
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.
to determine the value of RQJA
:
RQJA = RQJC + RQCS + RQSA
(3)
7
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
