Datasheet

LM2595

SNVS122B –MAY 1999–REVISED APRIL 2013

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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 in

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 3 in

, only small improvements in

heat dissipation are realized. If further thermal improvements are needed, double sided or multilayer PC-board

with large copper areas are recommended.

The curves shown in Figure 33 show the LM2595S (TO-263 package) junction temperature rise above ambient

temperature with a 1A 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.

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 surrounding air is still or moving. Furthermore, some of these components 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.

Circuit Data for Temperature Rise Curve

TO-220 Package (NDH)

Capacitors Through hole electrolytic

Inductor Through hole, Schott, 68 μH

Diode Through hole, 3A 40V, Schottky

PC board 3 square inches single sided 2 oz. copper (0.0028″)

Figure 32. Junction Temperature Rise, TO-220

Product Folder Links: LM2595