ZHCSJ62D December   2017  – July 2021 TLV767

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Pin Configuration and 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
  7. 7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1 Output Enable
      2. 8.3.2 Dropout Voltage
      3. 8.3.3 Foldback Current Limit
      4. 8.3.4 Undervoltage Lockout (UVLO)
      5. 8.3.5 Output Pulldown
      6. 8.3.6 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Device Functional Mode Comparison
      2. 8.4.2 Normal Operation
      3. 8.4.3 Dropout Operation
      4. 8.4.4 Disabled
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Adjustable Device Feedback Resistors
      2. 9.1.2 Recommended Capacitor Types
      3. 9.1.3 Input and Output Capacitor Requirements
      4. 9.1.4 Reverse Current
      5. 9.1.5 Feed-Forward Capacitor (CFF)
      6. 9.1.6 Power Dissipation (PD)
      7. 9.1.7 Estimating Junction Temperature
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Transient Response
        2. 9.2.2.2 Choose Feedback Resistors
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Device Nomenclature
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 接收文档更新通知
    4. 12.4 支持资源
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 术语表

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9.1.5 Feed-Forward Capacitor (CFF)

For the adjustable-voltage version device, a feed-forward capacitor (CFF) can be connected from the OUT pin to the FB pin. CFF improves transient, noise, and PSRR performance, but is not required for regulator stability. Recommended CFF values are listed in the Recommended Operating Conditions table. A higher capacitance CFF can be used; however, the start-up time increases. For a detailed description of CFF tradeoffs, see the Pros and Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator application report.

CFF and R1 form a zero in the loop gain at frequency fZ, while CFF, R1, and R2 form a pole in the loop gain at frequency fP. CFF zero and pole frequencies can be calculated from the following equations:

Equation 4. fZ = 1 / (2 × π × CFF × R1)
Equation 5. fP = 1 / (2 × π × CFF × (R1 || R2))

CFF ≥ 10 pF is required for stability if the feedback divider current is less than 5 µA. Equation 6 calculates the feedback divider current.

Equation 6. IFB_Divider = VOUT / (R1 + R2)

To avoid start-up time increases from CFF, limit the product CFF × R1 < 50 µs.

For an output voltage of 0.8 V with the FB pin tied to the OUT pin, no CFF is used.