Datasheet

LM1117-N, LM1117I

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SNOS412M –FEBRUARY 2000–REVISED MARCH 2013

Figure 22. Regulator with Protection Diode

HEATSINK REQUIREMENTS

When an integrated circuit operates with an 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-dimensional steady-state model of conduction heat transfer is

demonstrated in Figure 23. 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.

Rθ

(Component Variables) Rθ

(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

Ambient Temperatue

Shape of Mounting Pad

The case temperature is measured at the point where the leads contact with the mounting pad surface

Figure 23. Cross-Sectional View of Integrated Circuit Mounted on a Printed Circuit Board

The LM1117-N regulators have internal thermal shutdown to protect the device from over-heating. Under all

possible operating conditions, the junction temperature of the LM1117-N must be within the range of 0°C to

125°C. A heatsink may be required depending on the maximum power dissipation and maximum ambient

temperature of the application. To determine if a heatsink is needed, the power dissipated by the regulator, P

must be calculated:

= I

+ I

(2)

Product Folder Links: LM1117-N LM1117I