NUD4001, NSVD4001

http://onsemi.com

7

THERMAL INFORMATION

NUD4001, NSVD4001 Power Dissipation

The power dissipation of the SO−8 is a function of the 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

can be calculated as follows:

PD +

TJmax * TA

RqJA

The values for the equation are found in the maximum

ratings table on the data sheet. Substituting these values into

calculate the power dissipation of the device which in this

case is 1.13 W.

PD + 150° C * 25° C

110° C

+ 1.13 W

The 110

°C/W for the SO−8 package assumes the use of a

FR−4 copper board with an area of 2 square inches with 2 oz

coverage to achieve a power dissipation of 1.13 W. There are

other alternatives to achieving higher dissipation from the

SOIC package. One of them is to increase the copper area to

reduce the thermal resistance. Figure 11 shows how the

thermal resistance changes for different copper areas.

Another alternative would be to use a ceramic substrate or

an aluminum core board such as Thermal Clad

®. Using a

board material such as Thermal Clad or an aluminum core

board, the power dissipation can be even doubled using the

same footprint.

60

80

100

120

140

160

180

0

1

23

4

5

678

9

10

Figure 11. qJA versus Board Area

0

50

100

150

200

250

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

TIME (sec)

1S −36.9 sq. mm −0.057 in sq.

1S −75.8 sq. mm −0.117 in sq.

1S −150.0 sq. mm −0.233 in sq.

1S −321.5 sq. mm −0.498 in sq.

1S −681.0 sq. mm −1.056 in sq.

1S −1255.0 sq. mm −1.945 in sq.

Figure 12. Transient Thermal Response