LM6321 datasheet(8/11 Pages) NSC

8 / 11 page

Application Hints (Continued)

pation in any application is P

D =(TJ(max)−TA)/

JA. For the

simple case of a buffer driving a resistive load as in Figure 2,

the maximum DC power dissipation occurs when the output

is at half the supply. Assuming equal supplies, the formula is

D =IS (2V

+)+V+2/4 R

The next parameter which must be calculated is the maxi-

mum allowable temperature rise, T

R(max). This is calculated

by using the formula:

R(max) = TJ(max) − TA(max)

where: T

J(max)

the

maximum

allowable

junction

temperature

A(max) is the maximum ambient temperature

Using the calculated values for T

R(max) and P(max), the

required value for junction-to-ambient thermal resistance,

(J–A), can now be found:

(J–A) =TR(max)/P(max)

The heatsink for the LM6321 is made using the PC board

copper. The heat is conducted from the die, through the lead

frame (inside the part), and out the pins which are soldered

to the PC board. The pins used for heat conduction are:

TABLE 1.

Part

Package

Pins

LM6321N

8-Pin DIP

1, 4, 5, 8

LM6321M

14-Pin SO

1, 2, 3, 6, 7,

8, 9, 13, 14

Figure 3 shows copper patterns which may be used to

dissipate heat from the LM6321.

TABLE 2.

Package

L (in.)

H (in.)

JA (˚C/W)

8-Pin DIP

0.5

14-Pin SO

0.5

Table 2 shows some values of junction-to-ambient thermal

resistance (

JA) for values of L and W for 2 oz. copper:

00922308

FIGURE 2.

8-Pin DIP

00922309

14-Pin SOIC

00922310

*For best results, useL=2H

FIGURE 3. Copper Heatsink Patterns

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