lm9070t National Semiconductor Corporation, lm9070t Datasheet - Page 12

• Manufacturer Part Number: lm9070t
• Description: Low-dropout System Voltage Regulator With Keep-alive On/off Control
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
THERMAL MANAGEMENT
The LM9070 is packaged in both a TO-263 surface mount
power package and a narrow lead-pitch TO-220 package. To
obtain operation over the highest possible load current and
input voltage ranges, care must be taken to control the
operating temperature of the device. Thermal shutdown pro-
tection is built in, with a threshold above 150˚C. Conven-
tional heat-sinking techniques can be used with the TO-220
package. When applying the TO-263 package, on board
heat-sinking is important to prevent premature thermal shut-
down. More copper foil area under the tab of the device will
directly improve the operating θ
which will reduce the junction temperature of the device.
The θ
heat sink) is rated at 80˚C/W. The effective θ
J-A
value for the TO-263 package (still air, no additional
J-A
of the TO-263 package,
FIGURE 3. Typical TO-263 PC Board Heatsinking
(Continued)
J-A
value of the
12
TO-263 package can be reduced by increasing the printed
circuit board area that is connected (soldered) to the pack-
age tab. Using 1 ounce (1.4 mils thick) copper clad with no
solder mask, an area of 0.5 square inches will reduce θ
50˚C/W, an area of 1.0 square inches will reduce θ
37˚C/W, and an area of 1.6 square inches will reduce θ
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 θ
The use of a double sided PC board with soldered filled vias
between two planes of copper, as shown in Figure 3, will
improve thermal performance while optimizing the PC board
surface area required. Using the double sided PC board
arrangement shown in Figure 3, 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 θ
43˚C/W.
01283127
J-A
rating.
J-A
J-A
J-A
J-A
to
to
to
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