SNVS129G May   2004  – June 2025 LM2675

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1  Absolute Maximum Ratings
    2. 5.2  ESD Ratings
    3. 5.3  Recommended Operating Conditions
    4. 5.4  Thermal Information
      1. 5.4.1 Electrical Characteristics – 3.3 V
    5. 5.5  Electrical Characteristics – 5 V
    6. 5.6  Electrical Characteristics – 12 V
    7. 5.7  Electrical Characteristics – Adjustable
    8. 5.8  Electrical Characteristics – All Output Voltage Versions
    9. 5.9  Typical Characteristics
    10. 5.10 Typical Characteristics – Fixed Output Voltage Versions
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Adjustable Output Voltage
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown Mode
      2. 6.4.2 Active Mode
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Fixed Output Voltage Application
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 Custom Design with WEBENCH® Tools
          2. 7.2.1.2.2 Inductor Selection (L1)
          3. 7.2.1.2.3 Output Capacitor Selection (COUT)
          4. 7.2.1.2.4 Catch Diode Selection (D1)
          5. 7.2.1.2.5 Input Capacitor (CIN)
          6. 7.2.1.2.6 Boost Capacitor (CB)
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Adjustable Output Voltage Application
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
          1. 7.2.2.2.1 Programming Output Voltage
          2. 7.2.2.2.2 Inductor Selection (L1)
          3. 7.2.2.2.3 Output Capacitor SeIection (COUT)
          4. 7.2.2.2.4 Catch Diode Selection (D1)
          5. 7.2.2.2.5 Input Capacitor (CIN)
          6. 7.2.2.2.6 Boost Capacitor (CB)
        3. 7.2.2.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 WSON Package Devices
      2. 7.4.2 Layout Examples
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design with WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
7.2.2.2.5 Input Capacitor (CIN)

A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input. This capacitor must be located close to the IC using short leads. In addition, the RMS current rating of the input capacitor must be selected to be at least ½ the DC load current. The capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The curves shown in Figure 7-2 show typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel connection of two or more capacitors can be required to increase the total minimum RMS current rating to suit the application requirements.

For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage. Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be twice the maximum input voltage. Table 7-9 and Table 7-5 show the recommended application voltage for AVX TPS and Sprague 594D tantalum capacitors. TI recommends that they be surge current tested by the manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small inductor in series with the input supply line.

Table 7-9 AVX TPS
RECOMMENDED APPLICATION VOLTAGEVOLTAGE RATING
85°C RATING
3.36.3
510
1020
1225
1535

Use caution when using ceramic capacitors for input bypassing, because it can cause severe ringing at the VIN pin.

The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 28 V, an aluminum electrolytic capacitor with a voltage rating of at least 35 V (1.25 × VIN) can be needed.

The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load current. In this example, with a 1-A load, a capacitor with a RMS current rating of at least 500 mA is needed. The curves shown in Figure 7-2 can be used to select an appropriate input capacitor. From the curves, locate the 35-V line and note which capacitor values have RMS current ratings greater than 500 mA.

For a through hole design, a 330-μF, 35-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or equivalent) can be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS, and the Nichicon WF or UR and the NIC Components NACZ series can be considered.

For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking Table 7-5, and the Sprague 594D series data sheet, a Sprague 594D 15-μF, 50-V capacitor is adequate.