SNVS574G July   2008  – July 2019 LM3421 , LM3423

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Boost Application
  4. 4 Revision History
  5. 5 Device Comparison
  6. 6 Pin Configuration and Functions
    1.     Pin 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 Electrical Characteristics
    6. 7.6 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  Current Regulators
      2. 8.3.2  Predictive Off-Time (PRO) Control
      3. 8.3.3  Average LED Current
      4. 8.3.4  Analog Dimming
      5. 8.3.5  Current Sense and Current Limit
      6. 8.3.6  Overcurrent Protection
      7. 8.3.7  Zero Current Shutdown
      8. 8.3.8  Control Loop Compensation
      9. 8.3.9  Start-Up Regulator
      10. 8.3.10 Overvoltage Lockout (OVLO)
      11. 8.3.11 Input Undervoltage Lockout (UVLO)
        1. 8.3.11.1 UVLO Only
        2. 8.3.11.2 PWM Dimming and UVLO
      12. 8.3.12 PWM Dimming
      13. 8.3.13 LM3423 Only: DPOL, FLT, TIMR, and LRDY
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Inductor
      2. 9.1.2 LED Dynamic Resistance
      3. 9.1.3 Output Capacitor
      4. 9.1.4 Input Capacitors
      5. 9.1.5 Main MOSFET / Dimming MOSFET
      6. 9.1.6 Re-Circulating Diode
      7. 9.1.7 Boost Inrush Current
      8. 9.1.8 Switching Frequency
    2. 9.2 Typical Applications
      1. 9.2.1 Basic Topology Schematics
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  Operating Point
          2. 9.2.1.2.2  Switching Frequency
          3. 9.2.1.2.3  Average LED Current
          4. 9.2.1.2.4  Inductor Ripple Current
          5. 9.2.1.2.5  LED Ripple Current
          6. 9.2.1.2.6  Peak Current Limit
          7. 9.2.1.2.7  Loop Compensation
          8. 9.2.1.2.8  Input Capacitance
          9. 9.2.1.2.9  N-channel FET
            1. 9.2.1.2.9.1 Boost and Buck-Boost
          10. 9.2.1.2.10 Diode
          11. 9.2.1.2.11 Output OVLO
          12. 9.2.1.2.12 Input UVLO
          13. 9.2.1.2.13 PWM Dimming Method
          14. 9.2.1.2.14 Analog Dimming Method
      2. 9.2.2 LM3421 Buck-Boost Application
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1  Operating Point
          2. 9.2.2.2.2  Switching Frequency
          3. 9.2.2.2.3  Average LED Current
          4. 9.2.2.2.4  Inductor Ripple Current
          5. 9.2.2.2.5  Output Capacitance
          6. 9.2.2.2.6  Peak Current Limit
          7. 9.2.2.2.7  Loop Compensation
          8. 9.2.2.2.8  Input Capacitance
          9. 9.2.2.2.9  N-channel FET
          10. 9.2.2.2.10 Diode
          11. 9.2.2.2.11 Input UVLO
          12. 9.2.2.2.12 Output OVLO
        3. 9.2.2.3 Application Curve
      3. 9.2.3 LM3421 BOOST Application
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
      4. 9.2.4 LM3421 Buck-Boost Application
        1. 9.2.4.1 Design Requirements
        2. 9.2.4.2 Detailed Design Procedure
      5. 9.2.5 LM3423 Boost Application
        1. 9.2.5.1 Design Requirements
        2. 9.2.5.2 Detailed Design Procedure
      6. 9.2.6 LM3421 Buck-Boost Application
        1. 9.2.6.1 Design Requirements
        2. 9.2.6.2 Detailed Design Procedure
      7. 9.2.7 LM3423 Buck Application
        1. 9.2.7.1 Design Requirements
        2. 9.2.7.2 Detailed Design Procedure
      8. 9.2.8 LM3423 Buck-Boost Application
        1. 9.2.8.1 Design Requirements
        2. 9.2.8.2 Detailed Design Procedure
      9. 9.2.9 LM3421 SEPIC Application
        1. 9.2.9.1 Design Procedure
        2. 9.2.9.2 Detailed Design Procedure
  10. 10Power Supply Recommendations
    1. 10.1 General Recommendations
    2. 10.2 Input Supply Current Limit
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Related Links
    3. 12.3 Community 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

9.2.2.2.12 Output OVLO

Solve for ROV2:

Equation 144. LM3421 LM3423 300673g9.gif

The closest standard resistor is 432 kΩ; therefore, VHYSO is:

Equation 145. LM3421 LM3423 300673h0.gif

Solve for ROV1:

Equation 146. LM3421 LM3423 300673h1.gif

The closest standard resistor is 13.7 kΩ, making VTURN-OFF:

Equation 147. LM3421 LM3423 300673h2.gif

The chosen components from step 12 are:

Equation 148. LM3421 LM3423 300673h3.gif

Table 2. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3421 Buck-boost controller TI LM3421MH
1 CBYP 2.2-µF X7R 10% 16V MURATA GRM21BR71C225KA12L
1 CCMP 0.33-µF X7R 10% 25V MURATA GRM21BR71E334KA01L
1 CFS 0.27-µF X7R 10% 25V MURATA GRM21BR71E274KA01L
4 CIN 4.7-µF X7R 10% 100V TDK C5750X7R2A475K
4 CO 10-µF X7R 10% 50V TDK C4532X7R1H106K
1 COV 47-pF COG/NPO 5% 50V AVX 08055A470JAT2A
1 CT 1000-pF COG/NPO 5% 50V MURATA GRM2165C1H102JA01D
1 D1 Schottky 100 V 12 A VISHAY 12CWQ10FNPBF
1 L1 33 µH 20% 6.3 A COILCRAFT MSS1278-333MLB
1 Q1 NMOS 100 V 32 A FAIRCHILD FDD3682
1 Q2 PNP 150 V 600 mA FAIRCHILD MMBT5401
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 RLIM 0.04 Ω 1% 1 W VISHAY WSL2512R0400FEA
1 ROV1 13.7 kΩ 1% VISHAY CRCW080513K7FKEA
1 ROV2 432 kΩ 1% VISHAY CRCW0805432KFKEA
1 RSNS 0.1 Ω 1% 1 W VISHAY WSL2512R1000FEA
1 RT 49.9 kΩ 1% VISHAY CRCW080549K9FKEA
1 RUV1 18.2 kΩ 1% VISHAY CRCW080518K2FKEA
1 RUV2 130 kΩ 1% VISHAY CRCW0805130KFKEA