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LM341, LM78M05

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SNVS090F – MAY 2004 – REVISED DECEMBER 2016

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Copyright © 2004–2016, Texas Instruments Incorporated

10 Layout

10.1 Layout Guidelines

Some layout guidelines must be followed to ensure proper regulation of the output voltage with minimum noise.

TI recommends that the input terminal be bypassed to ground with a bypass capacitor. The optimum placement

is closest to the input terminal of the device and the system GND. Take care to minimize the loop area formed by

the bypass-capacitor connection, the input terminal, and the system GND. Traces carrying the load current must

be wide to reduce the amount of parasitic trace inductance. In cases when VIN shorts to ground, an external

diode must be placed from VOUT to VIN to divert the surge current from the output capacitor and protect the IC.

This diode must be placed close to the corresponding IC pins to increase their effectiveness.

10.2 Layout Example

Figure 15. Layout Recommendation

10.3 Thermal Considerations

When an integrated circuit operates with appreciable current, its junction temperature is elevated. It is important

to quantify its thermal limits 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 16. 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.

There are several variables that may affect the thermal resistance and in turn the need for a heat sink, which

includes the following.

•

Leadframe size and material

•

Number of conduction pins

•

Die size

•

Die attach material

•

Molding compound size and material

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Mounting pad size, material, and location

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Placement of mounting pad

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PCB size and material

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Traces length and width

•

Adjacent heat sources

•

Volume of air

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Ambient temperature

•

Shape of mounting pad