SNVS570M January   2009  – November 2015 LM3445

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Overview of Phase Control Dimming
      2. 7.3.2  Theory of Operation
      3. 7.3.3  Sensing the Rectified TRIAC Waveform
      4. 7.3.4  LM3445 Line Sensing Circuitry
      5. 7.3.5  TRIAC Holding Current Resistor
      6. 7.3.6  Angle Detect
      7. 7.3.7  Bleeder
      8. 7.3.8  FLTR1 Pin
      9. 7.3.9  Dim Decoder
      10. 7.3.10 Valley-Fill Circuit
      11. 7.3.11 Valley-Fill Operation
      12. 7.3.12 Buck Converter
      13. 7.3.13 Overview of Constant Off-Time Control
      14. 7.3.14 Master/Slave Operation
      15. 7.3.15 Master/Slave Configuration
      16. 7.3.16 Master Board Modifications
      17. 7.3.17 Slave Board Modifications
      18. 7.3.18 Master/Slave Interconnection
      19. 7.3.19 Master/Slave Theory of Operation
      20. 7.3.20 Master/Slave Connection Diagram
      21. 7.3.21 Master/Slave Block Diagrams
      22. 7.3.22 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Determining Duty-Cycle (D)
      2. 8.1.2 Calculating Off-Time
      3. 8.1.3 Setting the Switching Frequency
      4. 8.1.4 Inductor Selection
      5. 8.1.5 Setting the LED Current
      6. 8.1.6 Valley Fill Capacitors
        1. 8.1.6.1 Determining the Capacitance Value of the Valley-Fill Capacitors
        2. 8.1.6.2 Determining Maximum Number of Series Connected LEDs Allowed
      7. 8.1.7 Output Capacitor
      8. 8.1.8 Switching MOSFET
      9. 8.1.9 Re-Circulating Diode
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Community Resources
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

1 Features

  • TRIAC Dim Decoder Circuit for LED Dimming
  • Application Voltage Range 80 VAC to 277 VAC
  • Capable of Controlling LED Currents Greater Than 1 A
  • Adjustable Switching Frequency
  • Low Quiescent Current
  • Adaptive Programmable Off-Time Allows for Constant Ripple Current
  • Thermal Shutdown
  • No 120-Hz Flicker
  • Low Profile 10-Pin VSSOP Package or 14-Pin SOIC
  • Patented Drive Architecture

2 Applications

  • Retro Fit TRIAC Dimming
  • Solid State Lighting
  • Industrial and Commercial Lighting
  • Residential Lighting

3 Description

The LM3445 is an adaptive constant off-time AC/DC buck (step-down) constant current controller designed to be compatible with TRIAC dimmers. The LM3445 provides a constant current for illuminating high power LEDs and includes a TRIAC dim decoder. The dim decoder allows wide range LED dimming using standard TRIAC dimmers. The high frequency capable architecture allows the use of small external passive components. The LM3445 includes a bleeder circuit to ensure proper TRIAC operation by allowing current flow while the line voltage is low to enable proper firing of the TRIAC. A passive PFC circuit ensures good power factor by drawing current directly from the line for most of the cycle, and provides a constant positive voltage to the buck regulator. Additional features include thermal shutdown, current limit and VCC under-voltage lockout.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM3445 VSSOP (10) 3.00 mm × 3.00 mm
SOIC (14) 3.91 mm × 8.65 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical LM3445 LED Driver Application Circuit

LM3445 30060301.gif

Efficiency vs Line Voltage

LM3445 30060305.gif