SLVSEW2A September   2020  – August 2021 TPS54618C-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed Frequency PWM Control
      2. 7.3.2  Slope Compensation and Output Current
      3. 7.3.3  Bootstrap Voltage (Boot) and Low Dropout Operation
      4. 7.3.4  Error Amplifier
      5. 7.3.5  Voltage Reference
      6. 7.3.6  Adjusting the Output Voltage
      7. 7.3.7  Enable and Adjusting Undervoltage Lockout
      8. 7.3.8  Soft-Start Pin
      9. 7.3.9  Sequencing
      10. 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
      11. 7.3.11 Overcurrent Protection
      12. 7.3.12 Frequency Shift
      13. 7.3.13 Reverse Overcurrent Protection
      14. 7.3.14 Synchronize Using the RT/CLK Pin
      15. 7.3.15 Power Good (PWRGD Pin)
      16. 7.3.16 Overvoltage Transient Protection
      17. 7.3.17 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Simple Small Signal Model for Peak Current Mode Control
      2. 7.4.2 Small Signal Model for Frequency Compensation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Step One: Select the Switching Frequency
        2. 8.2.2.2 Step Two: Select the Output Inductor
        3. 8.2.2.3 Step Three: Choose the Output Capacitor
        4. 8.2.2.4 Step Four: Select the Input Capacitor
        5. 8.2.2.5 Step Five: Choose the Soft-Start Capacitor
        6. 8.2.2.6 Step Six: Select the Bootstrap Capacitor
        7. 8.2.2.7 Step Eight: Select Output Voltage and Feedback Resistors
          1. 8.2.2.7.1 Output Voltage Limitations
        8. 8.2.2.8 Step Nine: Select Loop Compensation Components
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Power Dissipation Estimate
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Developmental Support
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.4.2 Small Signal Model for Frequency Compensation

The TPS54618C-Q1 uses a transconductance amplifier for the error amplifier and readily supports two of the commonly used frequency compensation circuits. The compensation circuits are shown in Figure 7-14. The Type-2 circuits are most likely implemented in high-bandwidth power supply designs using low-ESR output capacitors. In Type 2A, one additional high-frequency pole is added to attenuate high-frequency noise.

GUID-FD260D2C-2776-4C6D-A6F1-2B75D197A91A-low.gifFigure 7-14 Types of Frequency Compensation

The design guidelines for TPS54618C-Q1 loop compensation are as follows:

  1. The modulator pole, fpmod, and the esr zero, fz1, must be calculated using Equation 15 and Equation 16. Derating the output capacitor (COUT) can be needed if the output voltage is a high percentage of the capacitor rating. Use the capacitor manufacturer information to derate the capacitor value. Use Equation 17 and Equation 18 to estimate a starting point for the crossover frequency, fc. Equation 17 is the geometric mean of the modulator pole and the esr zero and Equation 18 is the mean of modulator pole and the switching frequency. Use the lower value of Equation 17 or Equation 18 as the maximum crossover frequency.
    Equation 15. GUID-FD67EB89-07F6-492B-92DD-8102A893690D-low.gif

    Equation 16. GUID-99949316-5507-4DA9-8D82-09F84FCBC80B-low.gif

    Equation 17. GUID-8E946A9E-1B8A-4293-8FC8-BD082E2127CF-low.gif

    Equation 18. GUID-E771D45E-F288-4D29-BB1D-8FD8D4FA4F39-low.gif

  2. R3 can be determined by Equation 19:
    Equation 19. GUID-44CB769E-677F-4E74-9F0F-B2A411ECC121-low.gif

    where

    • the gmea amplifier gain (245 μA/V)
    • gmps is the power stage gain (25 A/V)

  3. Place a compensation zero at the dominant pole:
    GUID-A729FBFC-CF5D-4839-921F-709CB69C130F-low.gif
    C1 can be determined by Equation 20:
    Equation 20. GUID-75759EF6-95F5-4274-9AE4-A58E6D642BA1-low.gif

  4. C2 is optional. It can be used to cancel the zero from the ESR of COUT.
    Equation 21. GUID-8C34E7DD-B5A0-4279-817F-0AC6CBAB9AC4-low.gif