ZHCS979F June   2012  – October 2020 TPS53318 , TPS53319

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 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
    6. 7.6 Typical Characteristics
    7. 7.7 TPS53319 Typical Characteristics
    8. 7.8 TPS53318 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  5-V LDO and VREG Start-Up
      2. 8.3.2  Adaptive On-Time D-CAP Control and Frequency Selection
      3. 8.3.3  Ramp Signal
      4. 8.3.4  Adaptive Zero Crossing
      5. 8.3.5  Output Discharge Control
      6. 8.3.6  Power-Good
      7. 8.3.7  Current Sense, Overcurrent, and Short Circuit Protection
      8. 8.3.8  Overvoltage and Undervoltage Protection
      9. 8.3.9  Redundant Overvoltage Protection (OVP)
      10. 8.3.10 UVLO Protection
      11. 8.3.11 Thermal Shutdown
      12. 8.3.12 Small Signal Model
      13. 8.3.13 External Component Selection Using All Ceramic Output Capacitors
    4. 8.4 Device Functional Modes
      1. 8.4.1 Enable, Soft Start, and Mode Selection
      2. 8.4.2 Auto-Skip Eco-mode Light Load Operation
      3. 8.4.3 Forced Continuous Conduction Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Application Using Bulk Output Capacitors, Redundant Overvoltage Protection Function (OVP) Disabled
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Step One: Select Operation Mode and Soft-Start Time
          2. 9.2.1.2.2 Step Two: Select Switching Frequency
          3. 9.2.1.2.3 Step Three: Choose the Inductor
          4. 9.2.1.2.4 Step Four: Choose the Output Capacitor or Capacitors
          5. 9.2.1.2.5 Step Five: Determine the Value of R1 and R2
          6. 9.2.1.2.6 Step Six: Choose the Overcurrent Setting Resistor
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Application Using Ceramic Output Capacitors, Redundant Overvoltage Protection Function (OVP) Enabled
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 External Component Selection Using All Ceramic Output Capacitors
          2. 9.2.2.2.2 Redundant Overvoltage Protection
        3. 9.2.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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8.3.12 Small Signal Model

From small-signal loop analysis, a buck converter using D-CAP mode can be simplified as shown in Figure 8-4.

GUID-BB6E855D-DCBD-474C-9168-9A8849D301A8-low.gif Figure 8-4 Simplified Modulator Model

The output voltage is compared with the internal reference voltage (ramp signal is ignored here for simplicity). The PWM comparator determines the timing to turn on the high-side MOSFET. The gain and speed of the comparator can be assumed high enough to keep the voltage at the beginning of each on cycle substantially constant.

Equation 6. GUID-E86B4E6E-E017-4185-9032-DEE11C3CA01A-low.gif

For loop stability, the 0-dB frequency, ƒ0, defined below needs to be lower than 1/4 of the switching frequency.

Equation 7. GUID-7B59C488-A043-4C5E-9684-203A257A8423-low.gif

According to Equation 7, the loop stability of D-CAP mode modulator is mainly determined by the chemistry of the capacitor. For example, specialty polymer capacitors (SP-CAP) have an output capacitance in the order of several 100 µF and ESR in range of 10 mΩ. These make ƒ0 on the order of 100 kHz or less, creating a stable loop. However, ceramic capacitors have an ƒ0 at more than 700 kHz, and need special care when used with this modulator. An application circuit for ceramic capacitor is described in Section 8.3.13.