LM9070 datasheet(12/19 Pages) TI1

12 / 19 page

LM9070

SNVS130E – DECEMBER 1999 – REVISED APRIL 2013

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The

θJ-A value for the TO-263 package (still air, no additional heat sink) is rated at 80°C/W. The effective θJ-A

value of the TO-263 package can be reduced by increasing the printed circuit board area that is connected

(soldered) to the package tab. Using 1 ounce (1.4 mils thick) copper clad with no solder mask, an area of 0.5

square inches will reduce

θJ-A to 50°C/W, an area of 1.0 square inches will reduce θJ-Ato 37°C/W, and an area of

1.6 square inches will reduce

θJ-A to 32°C/W. If the printed circuit board uses a solder mask, the copper clad area

under the solder mask should be increased by at least 50% to maintain a similar

θJ-A rating.

The use of a double sided PC board with soldered filled vias between two planes of copper, as shown in

Figure 24, will improve thermal performance while optimizing the PC board surface area required. Using the

double sided PC board arrangement shown in Figure 24, with 1 ounce (1.4 mils thick) copper clad with no solder

mask and solder filled vias, an area of 0.5 square inches on both sides will reduce

θJ-A to 43°C/W.

Figure 24. Typical TO-263 PC Board Heatsinking

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