SNVS470I January   2007  – November 2025 LM25576

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
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 High Voltage Start-Up Regulator
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown and Stand-by Mode
      2. 6.4.2 Oscillator and Sync Capability
      3. 6.4.3 Error Amplifier and PWM Comparator
      4. 6.4.4 RAMP Generator
      5. 6.4.5 Maximum Duty Cycle and Input Drop-Out Voltage
      6. 6.4.6 Current Limit
      7. 6.4.7 Soft Start
      8. 6.4.8 Boost Pin
      9. 6.4.9 Thermal Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Bias Power Dissipation Reduction
    2. 7.2 Typical Application
      1. 7.2.1 Typical Schematic for High Frequency (1 MHz) Application
      2. 7.2.2 Typical Schematic for Buck and Boost (Inverting) Application
      3. 7.2.3 Design Requirements
        1. 7.2.3.1  R3 (RT)
        2. 7.2.3.2  L1
        3. 7.2.3.3  C3 (CRAMP)
        4. 7.2.3.4  C9, C10
        5. 7.2.3.5  D1
        6. 7.2.3.6  C1, C2
        7. 7.2.3.7  C8
        8. 7.2.3.8  C7
        9. 7.2.3.9  C4
        10. 7.2.3.10 R5, R6
        11. 7.2.3.11 R1, R2, C12
        12. 7.2.3.12 R7, C11
        13. 7.2.3.13 R4, C5, C6
      4. 7.2.4 Detailed Design Procedure
        1. 7.2.4.1 Custom Design With WEBENCH® Tools
      5. 7.2.5 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 PCB Layout
      2. 7.4.2 Layout Example
      3. 7.4.3 Power Dissipation
      4. 7.4.4 Thermal Considerations
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Developmental 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

7.3 Power Supply Recommendations

The LM25576 converter is designed to operate from a wide input voltage range from 7V to 42V. The characteristics of the input supply must be compatible with the Absolute Maximum Ratings and Recommended Operating Conditions. In addition, establish that the input supply is capable of delivering the required input current to the fully-loaded regulator. Estimate the average input current with below equation:

Equation 15. I I N   =   V O U T   × I O U T V I N × η

where

η is the efficiency.

If the converter is connected to an input supply through long wires or PCB traces with large impedance, special care is required to achieve stable performance. The parasitic inductance and resistance of the input cables can have an adverse affect on converter operation. The parasitic inductance in combination with the low ESR ceramic input capacitors form an under-damped resonant circuit. This circuit can cause overvoltage transients at VIN each time the input supply is cycled ON and OFF. The parasitic resistance causes the input voltage to dip during a load transient. If the regulator is operating close to the minimum input voltage, this dip can cause false UVLO fault triggering and a system reset. The best way to solve such issues is to reduce the distance from the input supply to the regulator and use an aluminum or tantalum input capacitor in parallel with the ceramics.

The moderate ESR of the electrolytic capacitors helps to damp the input resonant circuit and reduce any voltage overshoots. A capacitance in the range of 10μF to 47μF is typically sufficient to provide input damping and helps to hold the input voltage steady during large load transients.

An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as well as some of the effects mentioned above. The AN-2162 Simple Success With Conducted EMI From DC-DC Converters application note provides helpful suggestions for designing an input filter for any switching regulator.