SLVS338T May   2001  – December 2022 TPS715

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  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.     Thermal Information
    5. 6.4 Electrical Characteristics
    6. 6.5 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Wide Supply Range
      2. 7.3.2 Low Quiescent Current
      3. 7.3.3 Dropout Voltage (VDO)
      4. 7.3.4 Current Limit
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Dropout Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1 Setting VOUT for the TPS71501 Adjustable LDO
        2. 8.2.1.2 External Capacitor Requirements
        3. 8.2.1.3 Input and Output Capacitor Requirements
        4. 8.2.1.4 Reverse Current
        5. 8.2.1.5 Feed-Forward Capacitor (CFF)
        6. 8.2.1.6 Power Dissipation (PD)
        7. 8.2.1.7 Estimating Junction Temperature
      2. 8.2.2 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Power Dissipation
      2. 8.5.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Evaluation Module
        2. 9.1.1.2 Spice Models
      2. 9.1.2 Device Nomenclature
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  10. 10Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.1.5 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 note.

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 1.205 V with the FB pin tied to the OUT pin, no CFF is used.