SNVS031M april   2000  – may 2023 LM2676

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: LM2676 – 3.3 V
    6. 6.6  Electrical Characteristics: LM2676 – 5 V
    7. 6.7  Electrical Characteristics: LM2676 – 12 B
    8. 6.8  Electrical Characteristics: LM2676 – Adjustable
    9. 6.9  Electrical Characteristics – All Output Voltage Versions
    10. 6.10 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 Switch Output
      2. 7.3.2 Input
      3. 7.3.3 C Boost
      4. 7.3.4 Ground
      5. 7.3.5 Feedback
      6. 7.3.6 ON/OFF
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Design Considerations
      2. 8.1.2 Inductor
      3. 8.1.3 Output Capacitor
      4. 8.1.4 Input Capacitor
      5. 8.1.5 Catch Diode
      6. 8.1.6 Boost Capacitor
      7. 8.1.7 Additional Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Application for All Output Voltage Versions
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Capacitor Selection Guides
          2. 8.2.1.2.2 Inductor Selection Guides
      2. 8.2.2 Application Curves
      3. 8.2.3 Fixed Output Voltage Application
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
          1. 8.2.3.2.1 Capacitor Selection
      4. 8.2.4 Adjustable Output Voltage Application
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedure
          1. 8.2.4.2.1 Capacitor Selection
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  10. 10Mechanical, Packaging, and Orderable Information
    1. 10.1 DAP (VSON Package)

Package Options

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

8.2.3.2 Detailed Design Procedure

A system logic power supply bus of 3.3 V is to be generated from a wall adapter which provides an unregulated DC voltage of 13 V to 16 V. The maximum load current is 2.5 A. Through-hole components are preferred.

Step 1: Operating conditions are:

  • VOUT = 3.3 V
  • VIN maximum = 16 V
  • ILOAD maximum = 2.5 A

Step 2: Select an LM2676T-3.3. The output voltage has a tolerance of ±2% at room temperature and ±3% over the full operating temperature range.

Step 3: Use the nomograph for the 3.3-V device (Figure 8-2). The intersection of the 16-V horizontal line (VIN max) and the 2.5-A vertical line (ILOAD max) indicates that L33, a 22-µH inductor, is required.

From Table 8-3, L33 in a through-hole component is available from Renco with part number RL-1283-22-43 or part number PE-53933 from Pulse Engineering.

Step 4: Use Table 8-5 or Table 8-6 to determine an output capacitor. With a 3.3-V output and a 22-µH inductor, there are four through-hole output capacitor solutions with the number of same type capacitors to be paralleled and an identifying capacitor code given. Table 8-1 or Table 8-2 provides the actual capacitor characteristics. Any of the following choices work in the circuit:

  • 1 × 220-µF, 10-V Sanyo OS-CON (code C5)
  • 1 × 1000-µF, 35-V Sanyo MV-GX (code C10)
  • 1 × 2200-µF, 10-V Nichicon PL (code C5)
  • 1 × 1000-µF, 35-V Panasonic HFQ (code C7)

Step 5: Use Table 8-7 or Table 8-8 to select an input capacitor. With a 3.3-V output and 22 µH, there are three through-hole solutions. These capacitors provide a sufficient voltage rating and an RMS current rating greater than 1.25 A (1/2 ILOAD max). Again, using Table 8-1 or Table 8-2 for specific component characteristics, the following choices are suitable:

  • 1 × 1000-µF, 63-V Sanyo MV-GX (code C14)
  • 1 × 820-µF, 63-V Nichicon PL (code C24)
  • 1 × 560-µF, 50-V Panasonic HFQ (code C13)

Step 6: From Table 8-4, a 3-A Schottky diode must be selected. For through-hole components, 20-V rated diodes are sufficient and two part types are suitable:

  • 1N5820
  • SR302

Step 7: A 0.01-µF capacitor is used for CBOOST.