LM341 Datasheet, PDF (6/11 Pages) National Semiconductor (TI) – 3-Terminal Positive Voltage Regulators

Typical Performance Characteristics (Continued)
Quiescent Current
Output Impedance
Line Transient Response
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Load Transient Response
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Design Considerations
The LM78MXX/LM341XX fixed voltage regulator series has
built-in thermal overload protection which prevents the de-
vice from being damaged due to excessive junction tem-
perature.
The regulators also contain internal short-circuit protection
which limits the maximum output current, and safe-area pro-
tection for the pass transistor which reduces the short-circuit
current as the voltage across the pass transistor is in-
creased.
Although the internal power dissipation is automatically lim-
ited, the maximum junction temperature of the device must
be kept below +125˚C in order to meet data sheet specifica-
tions. An adequate heatsink should be provided to assure
this limit is not exceeded under worst-case operating condi-
tions (maximum input voltage and load current) if reliable
performance is to be obtained).
1.0 Heatsink Considerations
When an integrated circuit operates with appreciable cur-
rent, its junction temperature is elevated. It is important to
quantify its thermal limits in order to achieve acceptable per-
formance and reliability. This limit is determined by summing
the individual parts consisting of a series of temperature
rises from the semiconductor junction to the operating envi-
ronment. A one-dimension steady-state model of conduction
heat transfer is demonstrated in The heat generated at the
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device junction flows through the die to the die attach pad,
through the lead frame to the surrounding case material, to
the printed circuit board, and eventually to the ambient envi-
ronment. Below is a list of variables that may affect the ther-
mal resistance and in turn the need for a heatsink.
R^θJC(Component Variables) R^θCA(Application Variables)
Leadframe Size & Material Mounting Pad Size, Material,
& Location
No. of Conduction Pins
Placement of Mounting Pad
Die Size
PCB Size & Material
Die Attach Material
Traces Length & Width
Molding Compound Size and Adjacent Heat Sources
Material
Volume of Air
Air Flow
Ambient Temperature
Shape of Mounting Pad
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