MMFT3055VL

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7

INFORMATION FOR USING THE SOT−223 SURFACE MOUNT PACKAGE

MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS

Surface mount board layout is a critical portion of the

total design. The footprint for the semiconductor packages

must be the correct size to insure proper solder connection

interface between the board and the package. With the

correct pad geometry, the packages will self align when

subjected to a solder reflow process.

0.079

2.0

0.15

3.8

0.248

6.3

0.079

2.0

0.059

1.5

0.059

1.5

0.059

1.5

0.091

2.3

0.091

2.3

mm

inches

SOT−223 POWER DISSIPATION

The power dissipation of the SOT−223 is a function of

the drain pad size. This can vary from the minimum pad

size for soldering to a pad size given for maximum power

dissipation. Power dissipation for a surface mount device is

the device junction to ambient, and the operating

follows:

The values for the equation are found in the maximum

ratings table on the data sheet. Substituting these values

one can calculate the power dissipation of the device which

in this case is 943 milliwatts.

175°C − 25°C

159°C/W

= 943 milliwatts

The 159°C/W for the SOT−223 package assumes the use

of the recommended footprint on a glass epoxy printed

circuit board to achieve a power dissipation of 943

milliwatts. There are other alternatives to achieving higher

power dissipation from the SOT−223 package. One is to

increase the area of the drain pad. By increasing the area of

the drain pad, the power dissipation can be increased.

Although one can almost double the power dissipation with

this method, one will be giving up area on the printed

circuit board which can defeat the purpose of using surface

shown in Figure 17.