REG113

10

SBVS031D

www.ti.com

POWER DISSIPATION

The REG113 is available in two different package configura-

tions. The ability to remove heat from the die is different for each

package type and, therefore, presents different considerations

in the printed circuit board (PCB) layout. On the MSOP-8

package, leads 5 through 8 are fused to the lead frame and may

be used to improve the thermal performance of the package.

The PCB area around the device that is free of other compo-

nents moves the heat from the device to the ambient air.

Although it is difficult or impossible to quantify all of the

variables in a thermal design of this type, performance data for

several simplified configurations are shown in Figure 6. In all

cases the PCB copper area is bare copper, free of solder resist

mask, and not solder plated. All examples are for 1-ounce

copper and in the case of the MSOP-8, the copper area is

connected to fused leads 5 to 8. See Figure 7 for thermal

resistance for varying areas of copper. Using heavier copper

can increase the effectiveness in removing the heat from the

device. In those examples where there is copper on both sides

of the PCB, no connection has been provided between the two

sides. The addition of plated through holes will improve the heat

sink effectiveness.

For large step changes in load current, the REG113 requires

a larger voltage drop across it to avoid degraded transient

response. The boundary of this transient dropout region is

drop above this line insure normal transient response.

In the transient dropout region between DC and Transient,

transient response recovery time increases. The time required to

recover from a load transient is a function of both the magnitude

and rate of the step change in load current and the available

to DC dropout levels), the REG113 can take several hundred

microseconds to re-enter the specified window of regulation.

TRANSIENT RESPONSE

The REG113 response to transient line and load conditions

improves at lower output voltages. The addition of a capacitor

(nominal value 0.47

µF) from the output pin to ground may

improve the transient response. In the adjustable version, the

output to the adjust pin also improves the transient response.

THERMAL PROTECTION

Power dissipated within the REG113 can cause the junction

temperature to rise, however, the REG113 has thermal

shutdown circuitry that protects the regulator from damage.

The thermal protection circuitry disables the output when

the junction temperature reaches approximately 160

°C,

allowing the device to cool. When the junction temperature

cools to approximately 140

°C, the output circuitry is again

enabled. Depending on various conditions, the thermal

protection circuit can cycle on and off. This limits the

dissipation of the regulator, but can have an undesirable

effect on the load.

Any tendency to activate the thermal protection circuit indi-

cates excessive power dissipation or an inadequate heat sink.

For reliable operation, junction temperature should be limited

to 125

°C, maximum. To estimate the margin of safety in a

complete design (including heat sink), increase the ambient

temperature until the thermal protection is triggered. Use

worst-case loads and signal conditions. For good reliability,

thermal protection should trigger more than 35

°C above the

maximum expected ambient condition of the application. This

produces a worst-case junction temperature of 125

°C at the

highest expected ambient temperature and worst-case load.

The internal protection circuitry of the REG113 is designed to

protect against overload conditions and is not intended to

replace proper heat sinking. Continuously running the REG113

into thermal shutdown will degrade reliability.

3.0

2.5

2.0

1.5

1.0

0.5

0

MAXIMUM POWER DISSIPATION vs TEMPERATURE

–50

–25

0

25

50

75

100

125

Ambient Temperature (

°C)

Condition 1

Condition 2

Condition 3

CONDITION

PACKAGE

PCB AREA

θ

JA

1

MSOP-8

1 sq. in. Cu, 1 Side

71

2

MSOP-8

0.25 sq. in. Cu, 1 Side

90

3

SOT-23-8

None

200

FIGURE 6. Maximum Power Dissipation versus Ambient Tem-

perature for the Various Packages and PCB Heat

Sink Configurations.