LM2596 datasheet(24/31 Pages) NSC

24 / 31 page

Application Information (Continued)

THERMAL CONSIDERATIONS

The LM2596 is available in two packages, a 5-pin TO-220

(T) and a 5-pin surface mount TO-263 (S).

The TO-220 package needs a heat sink under most condi-

tions. The size of the heatsink depends on the input voltage,

the output voltage, the load current and the ambient tem-

perature. The curves in

Figure 19 show the LM2596T junc-

tion temperature rises above ambient temperature for a 3A

load and different input and output voltages. The data for

these curves was taken with the LM2596T (TO-220 pack-

age) operating as a buck switching regulator in an ambient

temperature of 25˚C (still air). These temperature rise num-

bers are all approximate and there are many factors that can

affect these temperatures. Higher ambient temperatures re-

quire more heat sinking.

The TO-263 surface mount package tab is designed to be

soldered to the copper on a printed circuit board. The copper

and the board are the heat sink for this package and the

other heat producing components, such as the catch diode

and inductor. The PC board copper area that the package is

soldered to should be at least 0.4 in2, and ideally should

have 2 or more square inches of 2 oz. (0.0028) in) copper.

Additional copper area improves the thermal characteristics,

but with copper areas greater than approximately 6 in

2, only

small improvements in heat dissipation are realized. If fur-

ther thermal improvements are needed, double sided, mul-

tilayer PC board with large copper areas and/or airflow are

recommended.

The curves shown in

Figure 20 show the LM2596S (TO-263

package) junction temperature rise above ambient tempera-

ture with a 2A load for various input and output voltages. This

data was taken with the circuit operating as a buck switching

regulator with all components mounted on a PC board to

simulate the junction temperature under actual operating

conditions. This curve can be used for a quick check for the

approximate junction temperature for various conditions, but

be aware that there are many factors that can affect the

junction temperature. When load currents higher than 2A are

used, double sided or multilayer PC boards with large cop-

per areas and/or airflow might be needed, especially for high

ambient temperatures and high output voltages.

For the best thermal performance, wide copper traces and

generous amounts of printed circuit board copper should be

used in the board layout. (One exception to this is the output

(switch) pin, which should not have large areas of copper.)

Large areas of copper provide the best transfer of heat

(lower thermal resistance) to the surrounding air, and moving

air lowers the thermal resistance even further.

Package thermal resistance and junction temperature rise

numbers are all approximate, and there are many factors

that will affect these numbers. Some of these factors include

board size, shape, thickness, position, location, and even

board temperature. Other factors are, trace width, total

printed circuit copper area, copper thickness, single- or

double-sided, multilayer board and the amount of solder on

the board. The effectiveness of the PC board to dissipate

heat also depends on the size, quantity and spacing of other

components on the board, as well as whether the surround-

ing air is still or moving. Furthermore, some of these com-

ponents such as the catch diode will add heat to the PC

board and the heat can vary as the input voltage changes.

For the inductor, depending on the physical size, type of core

material and the DC resistance, it could either act as a heat

sink taking heat away from the board, or it could add heat to

the board.

01258334

Circuit Data for Temperature Rise Curve

TO-220 Package (T)

Capacitors

Through hole electrolytic

Inductor

Through hole, Renco

Diode

Through hole, 5A 40V, Schottky

PC board

3 square inches single sided 2 oz. copper

(0.0028")

FIGURE 19. Junction Temperature Rise, TO-220

01258335

Circuit Data for Temperature Rise Curve

TO-263 Package (S)

Capacitors

Surface mount tantalum, molded “D” size

Inductor

Surface mount, Pulse Engineering, 68 µH

Diode

Surface mount, 5A 40V, Schottky

PC board

9 square inches single sided 2 oz. copper

(0.0028")

FIGURE 20. Junction Temperature Rise, TO-263

LM2596 Datasheet(PDF) 24 Page - National Semiconductor (TI)

LM2596 Datasheet(HTML) 24 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Datasheet Download

Link URL