LP2960IM-3.3 National Semiconductor, LP2960IM-3.3 Datasheet - Page 13

• Manufacturer Part Number: LP2960IM-3.3
• Description: Adjustable Micropower 0.5A Low-Dropout Regulators
• Manufacturer: National Semiconductor

Application Hints
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
lated by using the formula:
where:
T
which is 125˚C for commercial grade parts.
T
encountered in the application.
Using the calculated values for T
mum allowable value for the junction-to-ambient thermal re-
sistance,
The heatsink for the LP2960 is made using the PC board
copper, with the heat generated on the die being conducted
through the lead frame and out to the pins which are sol-
dered to the PC board.
The GND pins are the only ones capable of conducting any
significant amount of heat, as they are internally attached to
the lead frame on which the die is mounted.
The figure below shows recommended copper foil patterns
to be used for heatsinking the DIP and Surface Mount pack-
ages:
J
A
(max) is the maximum ambient temperature which will be
(max) is the maximum allowable junction temperature,
(J−A)
T
R
, can now be found:
(max) = T
(J−A)
= T
J
(max) − T
R
(Continued)
(max)/P
R
(max) and P
R
(max). This is calcu-
A
D
(max)
D
, the maxi-
13
The table below shows measured values of
board with 1 ounce copper weight:
As the heat must transfer from the copper to the surrounding
air, best results (lowest
face copper layer with the solder resist opened up over the
heatsink area.
If an internal copper layer of a multi-layer board is used for
heatsinking, the board material acts as an insulator, inhibit-
ing heat transfer and increasing
As with any heatsink, increasing the airflow across the board
will significantly improve the heat transfer.
Package
Surface
Mount
DIP
Heat Sink Foil Patterns
L (in.)
1
2
1
2
J−A
) will be obtained by using a sur-
H (in.)
J−A
0.5
0.2
0.5
0.2
.
(J−A)
DS011962-31
J−A
www.national.com
50
52
72
74
(˚C/W)
for a PC