LP2952/LP2952A/LP2953/LP2953A
Schematic Diagram
01112706
Application Hints
HEATSINK REQUIREMENTS (Industrial Temperature
Range Devices)
The maximum allowable power dissipation for the LP2952/
LP2953 is limited by the maximum junction temperature
(+125˚C) and the external factors that determine how quickly
heat flows away from the part: the
ambient temperature
and
the
junction-to-ambient thermal resistance
for the specific
application.
The industrial temperature range (−40˚C
≤
T
J
≤
+125˚C)
parts are manufactured in plastic DIP and surface mount
packages which contain a copper lead frame that allows
heat to be effectively conducted away from the die, through
www.national.com
12
the ground pins of the IC, and into the copper of the PC
board. Details on heatsinking using PC board copper are
covered later.
To determine if a heatsink is required, the maximum power
dissipated by the regulator, P(max), must be calculated. It is
important to remember that if the regulator is powered from
a transformer connected to the AC line, the
maximum
specified AC input voltage
must be used (since this pro-
duces the maximum DC input voltage to the regulator).
shows the voltages and currents which are present
in the circuit. The formula for calculating the power dissi-
pated in the regulator is also shown in
NSC [ NATIONAL SEMICONDUCTOR ]
