SNOS412O February   2000  – June 2020 LM1117

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Adjustable Output Regulator
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 LM1117 Electrical Characteristics
    6. 7.6 LM1117I Electrical Characteristics
    7. 7.7 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Load Regulation
    4. 8.4 Device Functional Modes
      1. 8.4.1 Protection Diodes
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 External Capacitors
          1. 9.2.2.1.1 Input Bypass Capacitor
          2. 9.2.2.1.2 Adjust Terminal Bypass Capacitor
          3. 9.2.2.1.3 Output Capacitor
      3. 9.2.3 Application Curve
    3. 9.3 System Examples
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Heatsink Requirements
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

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 22. 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.

Table 1. Component and Application Variables

RθJC (COMPONENT VARIABLES) RθJA (APPLICATION VARIABLES)
Leadframe Size and Material Mounting Pad Size, Material, and Location
No. of Conduction Pins Placement of Mounting Pad
Die Size PCB Size and Material
Die Attach Material Traces Length and Width
Molding Compound Size and Material Adjacent Heat Sources
Volume of Air
Ambient Temperatue
Shape of Mounting Pad
LM1117 10091937.png
The case temperature is measured at the point where the leads contact with the mounting pad surface
Figure 22. Cross-Sectional View of Integrated Circuit Mounted on a Printed Circuit Board

The LM1117 regulators have internal thermal shutdown to protect the device from over-heating. Under all possible operating conditions, the junction temperature of the LM1117 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, PD , must be calculated:

Equation 2. IIN = IL + IG
Equation 3. PD = (VIN-VOUT)I L + VINIG

Figure 23 shows the voltages and currents which are present in the circuit.

LM1117 10091916.pngFigure 23. Power Dissipation Diagram

The next parameter which must be calculated is the maximum allowable temperature rise, TR(max):

Equation 4.  TR(max) = TJ(max)-TA(max)

where

  • TJ(max) is the maximum allowable junction temperature (125°C) which will be encountered in the application
  • TA(max) is the maximum ambient temperature which will be encountered in the application

Using the calculated values for TR(max) and PD, the maximum allowable value for the junction-to-ambient thermal resistance (RθJA) can be calculated:

Equation 5. RθJA = TR(max)/PD

For the maximum allowable value for θJA, refer to the Thermal Information table.

As a design aid, Table 2 shows the value of the θJA of SOT-223 and TO-252 for different heatsink area. Figure 24 and Figure 25 reflects the same test results as what are in the Table 2

Figure 26 and Figure 27 shows the maximum allowable power dissipation vs. ambient temperature for the SOT-223 and TO-252 device. Figure 28 and Figure 29 shows the maximum allowable power dissipation vs. copper area (in2) for the SOT-223 and TO-252 devices. Please see AN1028 for power enhancement techniques to be used with SOT-223 and TO-252 packages.

The AN-1187 Leadless Leadframe Package (LLP) application note discusses improved thermal performance and power dissipation for the WSON.

Table 2. RθJA Different Heatsink Area

LAYOUT COPPER AREA THERMAL RESISTANCE
Top Side (in2)(1) Bottom Side (in2) JA,°C/W) SOT-223 JA,°C/W) TO-252
1 0.0123 0 136 103
2 0.066 0 123 87
3 0.3 0 84 60
4 0.53 0 75 54
5 0.76 0 69 52
6 1 0 66 47
7 0 0.2 115 84
8 0 0.4 98 70
9 0 0.6 89 63
10 0 0.8 82 57
11 0 1 79 57
12 0.066 0.066 125 89
13 0.175 0.175 93 72
14 0.284 0.284 83 61
15 0.392 0.392 75 55
16 0.5 0.5 70 53
Tab of device attached to topside copper
LM1117 10091913.pngFigure 24. RθJA vs 1-oz Copper Area for SOT-223
LM1117 10091912.pngFigure 26. Maximum Allowable Power Dissipation vs Ambient Temperature for SOT-223
LM1117 10091914.pngFigure 28. Maximum Allowable Power Dissipation vs 1-oz Copper Area for SOT-223
LM1117 10091934.pngFigure 25. RθJA vs 2-oz Copper Area for TO-252
LM1117 10091936.pngFigure 27. Maximum Allowable Power Dissipation vs Ambient Temperature for TO-252
LM1117 10091935.pngFigure 29. Maximum Allowable Power Dissipation vs 2-oz Copper Area for TO-252
LM1117 10091941.pngFigure 30. Top View of the Thermal Test Pattern in Actual Scale
LM1117 10091942.pngFigure 31. Bottom View of the Thermal Test Pattern in Actual Scale