LM341-LM78M National Semiconductor, LM341-LM78M Datasheet - Page 6

• Manufacturer Part Number: LM341-LM78M
• Description: 3-Terminal Positive Voltage Regulators
• Manufacturer: National Semiconductor

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Typical Performance Characteristics
Quiescent Current
Line Transient Response
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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Output Impedance
Load Transient Response
(Continued)
6
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
Leadframe Size & Material
No. of Conduction Pins
Die Size
Die Attach Material
Molding Compound Size and
Material
JC
(Component Variables) R
Mounting Pad Size, Material,
& Location
Placement of Mounting Pad
PCB Size & Material
Traces Length & Width
Adjacent Heat Sources
Volume of Air
Air Flow
Ambient Temperature
Shape of Mounting Pad
CA
(Application Variables)
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