LM2596
www.ti.com
SNVS124C –NOVEMBER 1999–REVISED APRIL 2013
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 conditions. The size of the heatsink depends on the input
voltage, the output voltage, the load current and the ambient temperature. The curves in Figure 31 show the
LM2596T junction 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 package) operating as a buck
switching regulator in an ambient temperature of 25°C (still air). These temperature rise numbers are all
approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require
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 in2, only small improvements in
heat dissipation are realized. If further thermal improvements are needed, double sided, multilayer PC board with
large copper areas and/or airflow are recommended.
The curves shown in Figure 32 show the LM2596S (TO-263 package) junction temperature rise above ambient
temperature 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
copper 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 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.
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