LP2952 Datasheet, PDF (13/24 Pages) National Semiconductor (TI) – Adjustable Micropower Low-Dropout Voltage Regulators

Schematic Diagram
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
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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).
Figure 1 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 Figure 1:
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