SNOS412Q February   2000  – January 2023 LM1117

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 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. 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. 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
    4. 9.4 Power Supply Recommendations
    5. 9.5 Layout
      1. 9.5.1 Layout Guidelines
        1. 9.5.1.1 Heat Sink Requirements
      2. 9.5.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

9.5.1.1 Heat Sink Requirements

When an integrated circuit operates with an appreciable current, the junction temperature is elevated. The thermal limits must be quantified 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 9-9. 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 heat sink.

Table 9-1 Component and Application Variables
RθJC (COMPONENT VARIABLES)RθJA (Application Variables)
Lead frame size and materialMounting pad size, material, and location
No. of conduction pinsPlacement of mounting pad
Die sizePCB size and material
Die attach materialTraces length and width
Molding compound size and materialAdjacent heat sources
Volume of air
Ambient temperature
Shape of mounting pad
GUID-71AFDFB1-E5FC-4AD0-A391-F7158D09CC28-low.png
The case temperature is measured at the point where the leads contact with the mounting pad surface
Figure 9-9 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 heat sink can be required depending on the maximum power dissipation and maximum ambient temperature of the application. To determine if a heat sink 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 9-10 shows the voltages and currents which are present in the circuit.

GUID-DE732AA5-084E-420A-B288-0B94CC23DA99-low.pngFigure 9-10 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 is encountered in the application
  • TA(max) is the maximum ambient temperature which is 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, see the Section 7.4 table.

As a design aid, Table 9-2 shows the value of the θJA of SOT-223 and TO-252 for different heat sink area. Figure 9-11 and Figure 9-12 reflects the same test results as what are in the Table 9-2

Figure 9-13 and Figure 9-14 shows the maximum allowable power dissipation vs. ambient temperature for the SOT-223 and TO-252 device. Figure 9-15 and Figure 9-16 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 9-2 RθJA Different Heat Sink Area
LAYOUTCOPPER AREATHERMAL RESISTANCE
Top Side (in2)(1)Bottom Side (in2)(θJA,°C/W) SOT-223(θJA,°C/W) TO-252
10.01230136103
20.066012387
30.308460
40.5307554
50.7606952
6106647
700.211584
800.49870
900.68963
1000.88257
11017957
120.0660.06612589
130.1750.1759372
140.2840.2848361
150.3920.3927555
160.50.57053
(1) Tab of device attached to topside copper
GUID-1CC42D88-B26F-40CA-80D8-4DCFC0DE626A-low.pngFigure 9-11 RθJA vs 1-oz Copper Area for SOT-223
GUID-46BA5F65-8BE8-4870-99E5-B8D16B511249-low.pngFigure 9-13 Maximum Allowable Power Dissipation vs Ambient Temperature for SOT-223
GUID-05651241-88AD-4390-8C24-C9C036200A94-low.pngFigure 9-15 Maximum Allowable Power Dissipation vs 1-oz Copper Area for SOT-223
GUID-B826476F-CC87-4381-8881-89FFF71E5028-low.pngFigure 9-12 RθJA vs 2-oz Copper Area for TO-252
GUID-41028968-0E17-4E5A-96A4-928FD16E7738-low.pngFigure 9-14 Maximum Allowable Power Dissipation vs Ambient Temperature for TO-252
GUID-73045699-2891-4611-8272-A085AF45A039-low.pngFigure 9-16 Maximum Allowable Power Dissipation vs 2-oz Copper Area for TO-252
GUID-06B6DCF2-F37F-4087-A4D5-D839ADBF3815-low.pngFigure 9-17 Top View of the Thermal Test Pattern in Actual Scale
GUID-C84F4186-2640-43DA-AC3B-52AC18E3638F-low.pngFigure 9-18 Bottom View of the Thermal Test Pattern in Actual Scale