Datasheet

LM341/LM78MXX
www.ti.com SNVS090E –MAY 2004–REVISED AUGUST 2005
DESIGN CONSIDERATIONS
The LM78MXX/LM341XX fixed voltage regulator series has built-in thermal overload protection which prevents
the device from being damaged due to excessive junction temperature.
The regulators also contain internal short-circuit protection which limits the maximum output current, and safe-
area protection for the pass transistor which reduces the short-circuit current as the voltage across the pass
transistor is increased.
Although the internal power dissipation is automatically limited, the maximum junction temperature of the device
must be kept below +125°C in order to meet data sheet specifications. An adequate heatsink should be provided
to assure this limit is not exceeded under worst-case operating conditions (maximum input voltage and load
current) if reliable performance is to be obtained).
HEATSINK CONSIDERATIONS
When an integrated circuit operates with appreciable current, its junction temperature is elevated. It is important
to quantify its thermal limits in order to achieve acceptable performance 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 environment. A one-dimension steady-state model of conduction heat transfer is demonstrated in
Figure 14 The heat generated at the 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 environment.
Below is a list of variables that may affect the thermal 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 Material Adjacent Heat Sources
Volume of Air
Air Flow
Ambient Temperature
Shape of Mounting Pad
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