CS5253B−8

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7

Figure 16. Remote Sense

CS5253B−8

GND

100

mF

+5.0 V

+3.3 V

+Load

Optional

GND

+

10

mF

+

33

mF

+

+

Local

Connections

Remote

Connections

−Load

Calculating Power Dissipation and Heatsink

Requirements

High power regulators such as the CS5253B−8 usually

operate at high junction temperatures. Therefore, it is

important to calculate the power dissipation and junction

temperatures accurately to ensure that an adequate heatsink

CS5253B−8, electrical isolation may be required for some

applications. Also, as with all high power packages, thermal

compound in necessary to ensure proper heat flow. For

added safety, this high current LDO includes an internal

thermal shutdown circuit

The thermal characteristics of an IC depend on the

following four factors: junction temperature, ambient

temperature, die power dissipation, and the thermal

resistance from the die junction to ambient air. The

maximum junction temperature can be determined by:

TJ(max) + TA(max) ) PD(max)

R

qJA

The maximum ambient temperature and the power

dissipation 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:

PD(max) + (VIN(max) * VOUT(min))IOUT(max)

) VIN(max)

IIN(max)

A heatsink 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

R

qJA + RqJC ) RqCS ) RqSA

D2PAK−5 package. For a high current regulator such as the

CS5253B−8 the majority of heat is generated in the power

package type, heatsink interface (is an insulator and thermal

grease used?), and the contact area between the heatsink and

the package. Once these calculations are complete, the

the proper heatsink selected. For further discussion on

heatsink selection, see our application note “Thermal

Management,” document number AND8036/D.