REG102

12

SBVS024F

www.ti.com

FIGURE 7. Maximum Power Dissipation versus Ambient Temperature for the Various Packages and PCB Heat Sink Configurations.

FIGURE 8. Thermal Resistance versus PCB Area for the Five-Lead SOT-223.

THERMAL RESISTANCE vs PCB COPPER AREA

180

160

140

120

100

80

60

40

20

0

012345

Circuit-Board Copper Area

REG102

SOT-223 Surface-Mount Package

REG102

Surface-Mount Package

1 oz. copper

2.5

2

1.5

1

0.5

0

0

25

50

75

125

100

Ambient Temperature (

°C)

DEVICE DISSIPATION vs TEMPERATURE

CONDITION

PACKAGE

PCB AREA

JA

1

SOT-223

4in2 Top Side Only

53

°C/W

2

SOT-223

0.5in2 Top Side Only

110

°C/W

3

SO-8

—

150

°C/W

4

SOT-23

—

200

°C/W

CONDITIONS

#1

#2

#3

#4

θ

POWER DISSIPATION

The REG102 is available in three different package configu-

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

each package type and, therefore, presents different consid-

erations in the printed circuit board (PCB) layout. The PCB

area around the device that is free of other components

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

it is difficult to impossible to quantify all of the variables in a

thermal design of this type, performance data for several

simplified configurations are shown in Figure 7. In all cases,

the PCB copper area is bare copper (free of solder resist

mask), not solder plated, and are for 1-ounce copper. Using

heavier copper will increase the effectiveness in moving 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.

Power dissipation depends on input voltage, load conditions,

and duty cycle and is equal to the product of the average

output current times the voltage across the output element,

PV

V

I

DIN

OUT

OUT

=•

(

–

)

(3)

Power dissipation can be minimized by using the lowest

possible input voltage necessary to assure the required

output voltage.

REGULATOR MOUNTING

The tab of the SOT-223 package is electrically connected to

ground. For best thermal performance, this tab must be

soldered directly to a circuit-board copper area. Increasing

the copper area improves heat dissipation, as shown in

Figure 8.

Although the tab of the SOT-223 is electrical ground, it is not

intended to carry current. The copper pad that acts as a heat

sink should be isolated from the rest of the circuit to prevent

current flow through the device from the tab to the ground

pin. Solder pad footprint recommendations for the various

REG102 devices are presented in Application Bulletin

Solder

Pad Recommendations for Surface-Mount Devices

(SBFA015), available from the Texas Instruments web site

(www.ti.com).