SNVS118F december   1999  – may 2023 LM2594 , LM2594HV

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Description (continued)
  7. 6 Pin Configuration and Functions
  8. 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 – 3.3 V
    6. 7.6  Electrical Characteristics – 5 V
    7. 7.7  Electrical Characteristics – 12 V
    8. 7.8  Electrical Characteristics – Adjustable
    9. 7.9  Electrical Characteristics – All Output Voltage Versions
    10. 7.10 Typical Characteristics
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Delayed Start-Up
      2. 8.3.2 Undervoltage Lockout
      3. 8.3.3 Inverting Regulator
      4. 8.3.4 Inverting Regulator Shutdown Methods
    4. 8.4 Device Functional Modes
      1. 8.4.1 Discontinuous Mode Operation
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Capacitor (CIN)
      2. 9.1.2 Output Capacitor (COUT)
      3. 9.1.3 Catch Diode
      4. 9.1.4 Inductor Selection
      5. 9.1.5 Output Voltage Ripple and Transients
      6. 9.1.6 Open Core Inductors
    2. 9.2 Typical Applications
      1. 9.2.1 Series Buck Regulator (Fixed Output)
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Custom Design with WEBENCH® Tools
          2. 9.2.1.2.2 Inductor Selection (L1)
          3. 9.2.1.2.3 Output Capacitor Selection (COUT)
          4. 9.2.1.2.4 Catch Diode Selection (D1)
          5. 9.2.1.2.5 Input Capacitor (CIN)
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Series Buck Regulator (Adjustable Output)
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Programming Output Voltage
          2. 9.2.2.2.2 Inductor Selection (L1)
          3. 9.2.2.2.3 Output Capacitor Selection (COUT)
          4. 9.2.2.2.4 Feedforward Capacitor (CFF)
          5. 9.2.2.2.5 Catch Diode Selection (D1)
          6. 9.2.2.2.6 Input Capacitor (CIN)
        3. 9.2.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
      3. 9.4.3 Thermal Considerations
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design with WEBENCH® Tools
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
9.2.1.2.3 Output Capacitor Selection (COUT)
  1. In the majority of applications, low ESR (Equivalent Series Resistance) electrolytic capacitors between 82 μF and 220 μF and low-ESR, solid tantalum capacitors between 15 μF and 100 μF provide the best results. This capacitor must be located close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 220 μF. For additional information, see Section 9.1.2.
  2. To simplify the capacitor selection procedure, see Figure 9-8 for quick design component selection. This table contains different input voltages, output voltages, and load currents, and lists various inductors and output capacitors that provides the best design solutions.

    From Figure 9-8, locate the 5-V output voltage section. In the load current column, choose the load current line that is closest to the current required for the application; for this example, use the 0.5-A line. In the maximum input voltage column, select the line that covers the input voltage required for the application; in this example, use the 15-V line. The rest of this line shows the recommended inductors and capacitors that provides the best overall performance.

    The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four different capacitor manufacturers. TI recommends using both the manufacturers and the manufacturer's series that are listed in Table 9-5.

    In this example, aluminum electrolytic capacitors from several different manufacturers are available with the range of ESR numbers needed:

      120-μF, 2-5V Panasonic HFQ Series

      120-μF, 2-5V Nichicon PL Series

  3. The capacitor voltage rating for electrolytic capacitors must be at least 1.5 times greater than the output voltage, and often require much higher voltage ratings to satisfy the low ESR requirements for low output ripple voltage.

    For a 5-V output, a capacitor voltage rating at least 7.5 V or more is required. But, in this example, even a low ESR, switching grade, 120-μF, 10-V aluminum electrolytic capacitor can exhibit approximately 400 mΩ of ESR (see Figure 9-2 for the ESR vs voltage rating). This amount of ESR can result in relatively high output ripple voltage. To reduce the ripple to 1% of the output voltage, or less, a capacitor with a higher voltage rating (lower ESR) must be selected. A 16-V or 25-V capacitor reduces the ripple voltage by approximately half.