SNVS499I February   2007  – November 2023 LM5116

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 Switching Characteristics
    7. 5.7 Typical Performance 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
      2. 6.3.2 Enable
      3. 6.3.3 UVLO
      4. 6.3.4 Oscillator and Sync Capability
      5. 6.3.5 Error Amplifier and PWM Comparator
      6. 6.3.6 Ramp Generator
      7. 6.3.7 Current Limit
      8. 6.3.8 HO Output
      9. 6.3.9 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 Soft-Start and Diode Emulation
  8. 7 Application and Implementation
    1. 7.1 Application Information
    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  Timing Resistor
        3. 7.2.2.3  Output Inductor
        4. 7.2.2.4  Current Sense Resistor
        5. 7.2.2.5  Ramp Capacitor
        6. 7.2.2.6  Output Capacitors
        7. 7.2.2.7  Input Capacitors
        8. 7.2.2.8  VCC Capacitor
        9. 7.2.2.9  Bootstrap Capacitor
        10. 7.2.2.10 Soft Start Capacitor
        11. 7.2.2.11 Output Voltage Divider
        12. 7.2.2.12 UVLO Divider
        13. 7.2.2.13 MOSFETs
        14. 7.2.2.14 MOSFET Snubber
        15. 7.2.2.15 Error Amplifier Compensation
        16. 7.2.2.16 Comprehensive Equations
          1. 7.2.2.16.1 Current Sense Resistor and Ramp Capacitor
          2. 7.2.2.16.2 Modulator Transfer Function
          3. 7.2.2.16.3 Error Amplifier Transfer Function
      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
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 Custom Design with WEBENCH® Tools
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 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

7.4.1 Layout Guidelines

In a buck regulator, the primary switching loop consists of the input capacitor, MOSFETs, and current sense resistor. Minimizing the area of this loop reduces the stray inductance and minimizes noise and possible erratic operation. The input capacitor must be placed as close as possible to the MOSFETs, with the VIN side of the capacitor connected directly to the high-side MOSFET drain, and the GND side of the capacitor connected as close as possible to the low-side source or current sense resistor ground connection. TI recommends a ground plane in the PC board as a means to connect the quiet end (input voltage ground side) of the input filter capacitors to the output filter capacitors and the PGND pin 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 to a topside copper area covering the entire underside of the device. Place several vias in this underside copper area to the ground plane.

The highest power dissipating components are the two power MOSFETs. The easiest way to determine the power dissipated in the MOSFETs is to measure the total conversion losses (PIN – POUT), then subtract the power losses in the output inductor and any snubber resistors. The resulting power losses are primarily in the switching MOSFETs.

If a snubber is used, the power loss can be estimated with an oscilloscope by observation of the resistor voltage drop at both turn-on and turn-off transitions. Assuming that the RC time constant is << 1 / fSW.

Equation 49. P = C ✕ V2 ✕ fSW

The regulator has an exposed thermal pad to aid power dissipation. Selecting MOSFETs with exposed pads aids the power dissipation of these devices. Careful attention to RDS(ON) at high temperature must be observed. Also, at 250 kHz, a MOSFET with low gate capacitance results in lower switching losses.