ZHCSBX0C december   2013  – may 2023 TPS65261 , TPS65261-1

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Adjusting the Output Voltage
      2. 7.3.2  Power Failure Detector
      3. 7.3.3  Enable and Adjusting Undervoltage Lockout
      4. 7.3.4  Soft-Start Time
      5. 7.3.5  Power Up Sequencing
        1. 7.3.5.1 External Power Sequencing
        2. 7.3.5.2 Automatic Power Sequencing
      6. 7.3.6  V7V Low Dropout Regulator and Bootstrap
      7. 7.3.7  Out-of-Phase Operation
      8. 7.3.8  Output Overvoltage Protection (OVP)
      9. 7.3.9  Slope Compensation
      10. 7.3.10 Overcurrent Protection
        1. 7.3.10.1 High-side MOSFET Overcurrent Protection
        2. 7.3.10.2 Low-side MOSFET Overcurrent Protection
      11. 7.3.11 Power Good
      12. 7.3.12 Adjustable Switching Frequency
      13. 7.3.13 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Pulse Skipping MODE (PSM)
  9. 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 Output Inductor Selection
        2. 8.2.2.2 Output Capacitor Selection
        3. 8.2.2.3 Input Capacitor Selection
        4. 8.2.2.4 Loop Compensation
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Parts
    2. 9.2 接收文档更新通知
    3. 9.3 支持资源
    4. 9.4 Trademarks
    5. 9.5 静电放电警告
    6. 9.6 术语表
  11. 10Mechanical, Packaging, and Orderable Information

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8.2.2.2 Output Capacitor Selection

There are three primary considerations for selecting the value of the output capacitor. The output capacitor determines the modulator pole, the output voltage ripple, and how the regulator responds to a large change in load current. The output capacitance needs to be selected based on the most stringent of these three criteria.

The desired response to a large change in the load current is the first criteria. The output capacitor needs to supply the load with current when the regulator cannot. This situation can occur if there are desired hold-up times for the regulator where the output capacitor must hold the output voltage above a certain level for a specified amount of time after the input power is removed. The regulator is also temporarily not able to supply sufficient output current if there is a large, fast increase in the current needs of the load such as a transition from no load to full load. The regulator usually needs two or more clock cycles for the control loop to see the change in load current and output voltage and adjust the duty cycle to react to the change. The output capacitor must be sized to supply the extra current to the load until the control loop responds to the load change. The output capacitance must be large enough to supply the difference in current for 2 clock cycles while only allowing a tolerable amount of drop in the output voltage. Equation 16 shows the minimum output capacitance necessary to accomplish this.

Equation 16. GUID-10004020-1B97-4843-BF88-70AF8F7D9B44-low.gif

Where ΔIout is the change in output current, fsw is the regulators switching frequency and ΔVout is the allowable change in the output voltage.

Equation 17 calculates the minimum output capacitance needed to meet the output voltage ripple specification. Where fsw is the switching frequency, Voripple is the maximum allowable output voltage ripple, and Ioripple is the inductor ripple current.

Equation 17. GUID-9DBD7116-4FF0-4A87-89AD-DB3BEBA08750-low.gif

Equation 18 calculates the maximum ESR an output capacitor can have to meet the output voltage ripple specification.

Equation 18. GUID-98288914-A235-444D-8DBD-C3237E5CA220-low.gif

Additional capacitance de-ratings for aging, temperature and DC bias must be factored in, which increases this minimum value. Capacitors generally have limits to the amount of ripple current they can handle without failing or producing excess heat. An output capacitor that can support the inductor ripple current must be specified. Some capacitor data sheets specify the root mean square (RMS) value of the maximum ripple current. Equation 19 can be used to calculate the RMS ripple current the output capacitor needs to support.

Equation 19. GUID-6A8E327C-6C92-40C3-9399-BB9B84C40127-low.gif