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

6 Pin Configuration and Functions

PWP Package
16-Pin HTSSOP
Top View
LM3421 LM3423 pwp16_snvsb95.gif
PWP Package
20-Pin HTSSOP
Top View
LM3421 LM3423 pinout_pwp20_slvsb95.gif

Pin Functions

PIN I/O(1) FUNCTION
NAME LM3423 LM3421
AGND 6 6 G Analog ground. Connect to PGND through the DAP copper pad to provide ground return for CSH, COMP, RCT, and TIMR.
COMP 3 3 I Compensation. Connect a capacitor to AGND to set the compensation.
CSH 4 4 I Current sense high. Connect a resistor to AGND to set the signal current. For analog dimming, connect a controlled current source or a potentiometer to AGND as detailed in the Analog Dimming section.
DDRV 13 9 O Dim gate drive output. Connect to the gate of the dimming MOSFET.
DPOL 12 — I Dim polarity. Connect to AGND if dimming with a series P-channel MOSFET or leave open when dimming with series N-channel MOSFET.
EN 2 2 I Enable. Connect to AGND for zero current shutdown or apply more than 2.4 V to enable device.
FLT 9 — I Fault flag. Connect to pullup resistor from VIN and N-channel MOSFET open-drain output is high when a fault condition is latched by the timer.
GATE 15 11 O Main gate drive output. Connect to the gate of the main switching MOSFET.
HSN 20 16 I LED current sense negative. Connect through a series resistor to the negative side of the LED current sense resistor.
HSP 19 15 I LED current sense positive. Connect through a series resistor to the positive side of the LED current sense resistor.
IS 17 13 I Main switch current sense. Connect to the drain of the main N-channel MOSFET switch for RDS-ON sensing or to a sense resistor installed in the source of the same device.
LRDY 11 — O LED ready flag. Connect to pullup resistor from VIN and N-channel MOSFET open-drain output pulls down when the LED current is not in regulation.
nDIM 8 8 I Dimming input and undervoltage protection. Connect a PWM signal for dimming as detailed in the PWM Dimming section and/or a resistor divider from VIN to program input undervoltage lockout (UVLO). Turnon threshold is 1.24 V and hysteresis for turnoff is provided by a 23-µA current source.
OVP 7 7 I Overvoltage protection. Connect to a resistor divider from VO to program output overvoltage lockout (OVLO). Turnoff threshold is 1.24 V and hysteresis for turnon is provided by 23-µA current source.
PGND 14 10 G Power ground. Connect to AGND through the DAP copper pad to provide ground return for GATE and DDRV.
RCT 5 5 I Resistor capacitor timing. External RC network sets the predictive off-time and thus the switching frequency.
RPD 18 14 I Resistor pulldown. Connect the low side of all external resistor dividers (VIN UVLO, OVP) to implement zero-current shutdown.
TIMR 10 — I Fault timer. Connect a capacitor to AGND to set the time delay before a sensed fault condition is latched.
VIN 1 1 I Input voltage. Bypass with 100-nF capacitor to AGND as close to the device as possible in the printed-circuit-board layout.
VCC 16 12 I Internal regulator output. Bypass with 2.2-µF to 3.3-µF ceramic capacitor to PGND.
Thermal PAD G Thermal PAD on bottom of IC. Star ground, connecting AGND and PGND.
DAP DAP (21) DAP (17) G Star ground, connecting AGND and PGND.
(1) G = Ground, I = Input, O = Output