mmft108t1 Freescale Semiconductor, Inc, mmft108t1 Datasheet - Page 3

• Manufacturer Part Number: mmft108t1
• Description: N?channel Enhancement?mode Logic Level
• Manufacturer: Freescale Semiconductor, Inc

design. The footprint for the semiconductor packages must
be the correct size to insure proper solder connection
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 determined
by T J(max) , the maximum rated junction temperature of the
die, R θJA , the thermal resistance from the device junction to
ambient, and the operating temperature, T A . Using the
values provided on the data sheet for the SOT-223 package,
P D can be calculated as follows:
ratings table on the data sheet. Substituting these values into
the equation for an ambient temperature T A of 25 C, one can
calculate the power dissipation of the device which in this
case is 0.8 watts.
of the recommended footprint on a glass epoxy printed circuit
board to achieve a power dissipation of 0.8 watts. There are
other alternatives to achieving higher power dissipation from
the SOT-223 package. One is to increase the area of the
collector pad. By increasing the area of the collector pad, the
power dissipation can be increased. Although the power
Motorola Small–Signal Transistors, FETs and Diodes Device Data
Surface mount board layout is a critical portion of the total
The power dissipation of the SOT-223 is a function of the
The values for the equation are found in the maximum
The 156 C/W for the SOT-223 package assumes the use
INFORMATION FOR USING THE SOT-223 SURFACE MOUNT PACKAGE
MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS
P D = 150 C – 25 C = 0.8 watts
P D =
156 C/W
T J(max) – T A
R θJA
0.079
2.0
SOT-223 POWER DISSIPATION
0.079
2.0
0.059
1.5
0.091
2.3
SOT-223
0.059
0.15
1.5
3.8
0.091
2.3
interface between the board and the package. With the
correct pad geometry, the packages will self align when
subjected to a solder reflow process.
dissipation can almost be doubled with this method, area is
taken up on the printed circuit board which can defeat the
purpose of using surface mount technology. A graph of R θJA
versus collector pad area is shown in Figure 9.
an aluminum core board such as Thermal Clad . Using a
board material such as Thermal Clad, an aluminum core
board, the power dissipation can be doubled using the same
footprint.
Another alternative would be to use a ceramic substrate or
0.059
160
140
120
100
1.5
80
0.0
Figure 3. Thermal Resistance versus Collector
*Mounted on the DPAK footprint
Pad Area for the SOT-223 Package (Typical)
0.248
6.3
Board Material = 0.0625
G-10/FR-4, 2 oz Copper
inches
mm
0.2
0.8 Watts
A, Area (square inches)
1.25 Watts*
0.4
0.6
MMFT108T1
T A = 25 C
0.8
1.5 Watts
1.0
3