SNVS553C January   2008  – November 2016 LM3407

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 Floating Buck Switching Converter
      2. 7.3.2 Pulse Level Modulation (PLM)
      3. 7.3.3 Internal VCC Regulator
      4. 7.3.4 Clock Generator
      5. 7.3.5 PWM Dimming of LED String
      6. 7.3.6 Input Under-Voltage Lock-Out (UVLO)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Low-Power Shutdown Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Switching Frequency Selection
      2. 8.1.2 LED Current Setting
      3. 8.1.3 Input and Output Capacitors
      4. 8.1.4 Selection of Inductor
      5. 8.1.5 Free-Wheeling Diode
    2. 8.2 Typical Applications
      1. 8.2.1 LM3407 Design Example
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Calculate RISNS
          2. 8.2.1.2.2 Calculate RFS
          3. 8.2.1.2.3 Choose L
          4. 8.2.1.2.4 Choose CIN and CVCC
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Typical Application for Driving 6 LEDs
      3. 8.2.3 Typical Application for Driving 1 LED
  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 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

10 Layout

10.1 Layout Guidelines

Because the copper traces of PCBs carry resistance and parasitic inductance, the longer the copper trace, the higher the resistance and inductance. These factors introduce voltage and current spikes to the switching nodes and may impair circuit performance. To optimize the performance of the LM3407, the rule of thumb is to keep the connections between components as short and direct as possible. Because true average current regulation is achieved by detecting the average switch current, the current setting resistor RISNS must be located as close as possible to the LM3407 to reduce the parasitic inductance of the copper trace and avoid noise pick-up. The connections between the LX pin, rectifier D1, inductor L1, and output capacitor COUT should be kept as short as possible to reduce the voltage spikes at the LX pin. TI recommends that CVCC, the output filter capacitor for the internal linear regulator of the LM3407, be placed close to the VCC pin. The input filter capacitor CIN should be located close to L1 and the cathode of D1. If CIN is connected to the VIN pin by a long trace, a 0.1-µF capacitor should be added close to VIN pin for noise filtering.

CAUTION

In normal operation, heat will be generated inside the LM3407 and may damage the device if no thermal management is applied. For more details on switching power supply layout considerations see AN-1149 Layout Guidelines for Switching Power Supplies (SNVA021).

10.2 Layout Example

LM3407 snvs553_layout.gif Figure 28. Layout Recommendation