Datasheet

REG104
11
SBVS025G
FIGURE 9. Maximum Power Dissipation versus Ambient
Temperature for the Various Packages and
PCB Heat Sink Configurations.
POWER DISSIPATION
The REG104 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 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. While it
is difficult to impossible to quantify all of the variables in a
thermal design of this type, performance data for several
configurations are shown in Figure 9. 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. 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 and load condi-
tions. Power dissipation is equal to the product of the aver-
age output current times the voltage across the output
element, V
IN
to V
OUT
voltage drop.
PVV I
DIN
OUT OUT AVG
=•( – )
()
Power dissipation can be minimized by using the lowest
possible input voltage necessary to assure the required
output voltage.
5
4
3
2
1
0
Power Dissipation (Watts)
0 25 50 75 125100
Ambient Temperature (°C)
CONDITIONS
#1
#2
#3
#4
CONDITION PACKAGE PCB AREA θ
JA
1 DDPAK 4in
2
Top Side Only 27°C/W
2 SOT-223 4in
2
Top Side Only 53°C/W
3 DDPAK None 65°C/W
4 SOT-223 0.5in
2
Top Side Only 110°C/W