SNVS429C October   2006  – December 2016 LM3405

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 Boost Function
      2. 7.3.2 Setting the LED Current
      3. 7.3.3 Output Voltage
      4. 7.3.4 Enable Mode or Shutdown Mode
      5. 7.3.5 LED PWM Dimming
      6. 7.3.6 Undervoltage Lockout
      7. 7.3.7 Current Limit
      8. 7.3.8 Overcurrent Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Thermal Shutdown
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Inductor (L1)
      2. 8.1.2 Input Capacitor (C1)
      3. 8.1.3 Output Capacitor (C2)
      4. 8.1.4 Feed-Forward Capacitor (C4)
      5. 8.1.5 Catch Diode (D1)
      6. 8.1.6 Boost Diode (D2)
      7. 8.1.7 Boost Capacitor (C3)
      8. 8.1.8 Power Loss Estimation
    2. 8.2 Typical Applications
      1. 8.2.1 VBOOST Derived from VIN (VIN = 5 V, IF = 1 A)
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Calculate Duty Cycle (D)
          2. 8.2.1.2.2 Choose Capacitor Values (C1, C2, C3, and C4)
          3. 8.2.1.2.3 Set the Nominal LED Current (R1)
          4. 8.2.1.2.4 Choose Diodes (D1 and D2)
          5. 8.2.1.2.5 Calculate the Inductor Value (L1)
        3. 8.2.1.3 Application Curve
    3. 8.3 System Examples
      1. 8.3.1 VBOOST Derived From VOUT (VIN = 12 V, IF = 1 A)
        1. 8.3.1.1 Bill of Materials
      2. 8.3.2 VBOOST Derived From VIN Through a Series Zener Diode, D3 (VIN = 15 V, IF = 1 A)
        1. 8.3.2.1 Bill of Materials
      3. 8.3.3 VBOOST Derived From VIN Through a Shunt Zener Diode, D3 (VIN = 15 V, IF = 1 A)
        1. 8.3.3.1 Bill of Materials
      4. 8.3.4 VBOOST Derived from VOUT Through a Series Zener Diode, D3 (VIN = 15 V, IF = 1 A)
        1. 8.3.4.1 Bill of Materials
  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 Resource
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

10 Layout

10.1 Layout Guidelines

When planning the layout there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration when completing the layout is the close coupling of the GND connections of the input capacitor C1 and the catch diode D1. These ground ends must be close to one another and be connected to the GND plane with at least two vias. Place these components as close to the IC as possible. The next consideration is the location of the GND connection of the output capacitor C2, which must be near the GND connections of C1 and D1.

There must be a continuous ground plane on the bottom layer of a two-layer board.

The FB pin is a high impedance node and take care to make the FB trace short to avoid noise pickup that causes inaccurate regulation. The LED current setting resistor R1 must be placed as close as possible to the IC, with the GND of R1 placed as close as possible to the GND of the IC. The VOUT trace to LED anode must be routed away from the inductor and any other traces that are switching.

High AC currents flow through the VIN, SW and VOUT traces, so they must be as short and wide as possible. Radiated noise can be decreased by choosing a shielded inductor.

The remaining components must also be placed as close as possible to the IC. See AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for further considerations.

10.2 Layout Example

LM3405 snvs429_layout.gif
Schematic in Figure 23
Figure 29. LM3405 Layout Example