AN1703 datasheet(6/22 Pages) STMICROELECTRONICS

6 / 22 page

AN1703 - APPLICATION NOTE

6/22

In free air we must consider the RTHJ-A and its value 100°C/W.

For the recommended footprint (45mm2) the RTHJ-PCB value is 62°C/W and the maximum allowable

power dissipation is:

For a drain pad area of 1in2 (about 600mm2) we obtain:

The next figure shows the maximum allowable power dissipation as function of a PCB drain pad area for

different TJ-TA values:

Figure 7: Maximum allowable power dissipation versus drain pad area

5. SOT-223

The SOT-223 is a small package designed for surface mount applications. The formed leads absorb

thermal stress during soldering, thereby eliminating the possibility of damage to the die. The

encapsulation material used in this package enhances the device reliability which allows it to exhibit

excellent performance in high temperature environments.

PCB

THj

150 =

∆

−

JMAX = 175°C, TC = 25°C)

PCB

THj

150 =

∆

−

JMAX = 175°C, TC = 25°C)

PCB

THJ

PCB

THJ

∆

⇒

−

200

400

600

800

1000

Tj-Ta=150°C

Tj-Ta=125°C

Tj-Ta=100°C

Tj-Ta=75°C

Tj-Ta=50°C

Area

mm2

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