LM2595 datasheet(32/43 Pages) TI1

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LM2595

SNVS122C – MAY 1999 – REVISED MAY 2016

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Layout Examples (continued)

CIN – 150-μF, 50-V aluminium electrolytic Nichicon, PL series

COUT – 120-μF, 25-V aluminium electrolytic Nichicon, PL series

D1 – 3-A, 40-V Schottky rectifier, 1N5822

L1 – 68-μH, L30, Schottky through-hole

R1 – 1-kΩ, 1%

R2 – Use formula in Detailed Design Procedure

CFF – See Table 7

Figure 39. Typical Through-Hole PCB Layout, Adjustable Output (1X Size)

11.3 Thermal Considerations

The LM2595 is available in two packages: a 5-pin TO-220 (NDH) and a 5-pin surface-mount TO-263 (KTT).

The TO-220 package can be used without a heat sink for ambient temperatures up to approximately 50°C

(depending on the output voltage and load current). Figure 40 shows the LM2595T junction temperature rises

above ambient temperature for different input and output voltages. The data tor these curves was taken with the

LM2595T (TO-220 package) operating as a 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 some heat sinking, either to the PCB or a small external heat

sink.

The TO-263 surface-mount package tab is designed to be soldered to the copper on a printed-circuit board

(PCB). 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 PCB copper area that the package is soldered to must be at least 0.4

in2, and ideally must 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 in2, only small improvements in

heat dissipation are realized. If further thermal improvements are required, TI recommends using double sided or

multilayer PCB with large copper areas.

Figure 41 show the LM2595S (TO-263 package) junction temperature rise above ambient temperature with a 1-A

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 PCB 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 PCB copper must be used in

the board layout. (One exception to this is the output (switch) pin, which must 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.

LM2595 Datasheet(PDF) 32 Page - Texas Instruments