4

Figure 2. Grounding scheme for the output regulator to minimize para-

sitics.

The CS5207-3 linear regulator includes thermal shutdown

and safe operating area circuitry to protect the device.

High power regulators such as this usually operate at high

junction temperatures so it is important to calculate the

power dissipation and junction temperatures accurately to

ensure that an adequate heat sink is used.

cal isolation may be required for some applications.

Thermal compound should always be used with high cur-

rent regulators such as these.

The thermal characteristics of an IC depend on the follow-

ing four factors:

These four are related by the equation

(1)

The maximum ambient temperature and the power dissi-

pation 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:

(2)

where

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

junction and the surrounding air.

3. Thermal Resistance of the Heat Sink to the ambient air,

These are connected by the equation:

(3)

result can be substituted in equation (1).

regulator such as the CS5207-3, the majority of the heat is

generated in the power transistor section. The value for

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 calcula-

tions are complete, the maximum permissible value of

For further discussion on heat sink selection, see applica-

tion note ÒThermal Management for Linear Regulators.Ó

Calculating Power Dissipation and Heat Sink Requirements

conductor parasitic

resistance

CS5207-3

Gnd

Applications Information: continued