SNOSB24C October   2008  – November 2025 LM5576-Q1

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 Shutdown / Standby
      2. 6.3.2 Soft Start
      3. 6.3.3 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 High Voltage Start-Up Regulator
      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 / Input Dropout Voltage
      6. 6.4.6 Boost Pin
      7. 6.4.7 Current Limit
  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 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Custom Design With WEBENCH® Tools
        2. 7.2.2.2  External Components
        3. 7.2.2.3  R3 (RT)
        4. 7.2.2.4  L1
        5. 7.2.2.5  C3 (CRAMP)
        6. 7.2.2.6  C9, C10
        7. 7.2.2.7  D1
        8. 7.2.2.8  C1, C2
        9. 7.2.2.9  C8
        10. 7.2.2.10 C7
        11. 7.2.2.11 C4
        12. 7.2.2.12 R5, R6
        13. 7.2.2.13 R1, R2, C12
        14. 7.2.2.14 R7, C11
        15. 7.2.2.15 R4, C5, C6
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      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 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

7.4.1 Layout Guidelines

The circuit in Figure 7-3 serves as both a block diagram of the LM5576-Q1 and a typical application board schematic for the LM5576-Q1. In a buck regulator, there are two loops where currents are switched very fast. The first loop starts from the input capacitors, to the regulator VIN pin, to the regulator SW pin, to the inductor, and then out to the load. The second loop starts from the output capacitor ground, to the regulator PGND pins, to the regulator IS pins, to the diode anode, to the inductor, and then out to the load. Minimize the loop area of these two loops to reduce the stray inductance and minimizes noise and possible erratic operation. A ground plane in the printed-circuit board (PCB) is recommended as a means to connect the input filter capacitors to the output filter capacitors and the PGND pins of the regulator. Connect all of the low power ground connections (CSS, RT, CRAMP) directly to the regulator AGND pin. Connect the AGND and PGND pins together through the topside copper area covering the entire underside of the device. Place several vias in this underside copper area to the ground plane.

The two highest power dissipating components are the re-circulating diode and the LM5576-Q1 regulator IC. The easiest method to determine the power dissipated within the LM5576-Q1 is to measure the total conversion losses (PIN – POUT) then subtract the power losses in the Schottky diode, output inductor and snubber resistor. Use Equation 20 to calculate an approximation for the Schottky diode loss.

Equation 20. P = (1 – D) × IOUT × VFWD

Use Equation 21 to calculate an approximation for the output inductor power.

Equation 21. P = IOUT2 × R × 1.1

where

  • R is the DC resistance of the inductor
  • and the 1.1 factor is an approximation for the AC losses.

If a snubber is used, use Equation 22 to calculate an approximation for the damping resistor power dissipation.

Equation 22. P = VIN2 × Fsw × Csnub

where

  • Fsw is the switching frequency
  • and Csnub is the snubber capacitor.

The regulator has an exposed thermal pad to help power dissipation. Add several vias under the device to the ground plane to greatly reduce the regulator junction temperature. Select a diode with an exposed pad to help the power dissipation of the diode.