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

5 Pin Configuration and Functions

DGS Package
10-Pin VSSOP
Top View
LM3445 30060303.gif
D Package
14-Pin SOIC
Top View
LM3445 30060373.gif

Pin Functions

PIN I/O DESCRIPTION
NAME SOIC VSSOP
ASNS 12 1 O PWM output of the TRIAC dim decoder circuit. Outputs a 0 to 4-V PWM signal with a duty cycle proportional to the TRIAC dimmer on-time.
BLDR 10 10 I Bleeder pin. Provides the input signal to the angle detect circuitry as well as a current path through a switched 230-Ω resistor to ensure proper firing of the TRIAC dimmer.
COFF 1 4 I OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant OFF time of the switching controller.
DIM 14 3 I/O Input/output dual function dim pin. This pin can be driven with an external PWM signal to dim the LEDs. It may also be used as an output signal and connected to the DIM pin of other LM3445s or other LED drivers to dim multiple LED circuits simultaneously.
FLTR1 13 2 I First filter input. The 120-Hz PWM signal from ASNS is filtered to a DC signal and compared to a 1 to 3 V, 5.85-kHz ramp to generate a higher frequency PWM signal with a duty cycle proportional to the TRIAC dimmer firing angle. Pull above 4.9-V (typical) to tri-state DIM.
FLTR2 3 5 I Second filter input. A capacitor tied to this pin filters the PWM dimming signal to supply a DC voltage to control the LED current. Could also be used as an analog dimming input.
GATE 8 8 O Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck controller.
GND 4 6 — Circuit ground connection
ISNS 7 7 I LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the maximum LED current.
N/C 2, 5, 6, 11 — — No Connect
VCC 9 9 O Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.