ZHCSH45B June   2017  – October 2021 TPS7A83A

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 说明（续）
  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: General
    6. 7.6 Electrical Characteristics: TPS7A8300A
    7. 7.7 Electrical Characteristics: TPS7A8301A
    8. 7.8 Typical Characteristics: TPS7A8300A
    9. 7.9 Typical Characteristics: TPS7A8301A
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Voltage Regulation Features
        1. 8.3.1.1 DC Regulation
        2. 8.3.1.2 AC and Transient Response
      2. 8.3.2 System Start-Up Features
        1. 8.3.2.1 Programmable Soft-Start (NR/SS)
        2. 8.3.2.2 Internal Sequencing
          1. 8.3.2.2.1 Enable (EN)
          2. 8.3.2.2.2 Undervoltage Lockout (UVLO) Control
          3. 8.3.2.2.3 Active Discharge
        3. 8.3.2.3 Power-Good Output (PG)
      3. 8.3.3 Internal Protection Features
        1. 8.3.3.1 Foldback Current Limit (ICL)
        2. 8.3.3.2 Thermal Protection (Tsd)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Regulation
      2. 8.4.2 Disabled
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 External Component Selection
        1. 9.1.1.1 Adjustable Operation
        2. 9.1.1.2 ANY-OUT Programmable Output Voltage
        3. 9.1.1.3 ANY-OUT Operation
        4. 9.1.1.4 Increasing ANY-OUT Resolution for LILO Conditions
        5. 9.1.1.5 Recommended Capacitor Types
        6. 9.1.1.6 Input and Output Capacitor Requirements (CIN and COUT)
        7. 9.1.1.7 Feed-Forward Capacitor (CFF)
        8. 9.1.1.8 Noise-Reduction and Soft-Start Capacitor (CNR/SS)
      2. 9.1.2 Start Up
        1. 9.1.2.1 Soft-Start (NR/SS)
          1. 9.1.2.1.1 Inrush Current
        2. 9.1.2.2 Undervoltage Lockout (UVLO)
        3. 9.1.2.3 Power-Good (PG) Function
      3. 9.1.3 AC and Transient Performance
        1. 9.1.3.1 Power-Supply Rejection Ratio (PSRR)
        2. 9.1.3.2 Output Voltage Noise
        3. 9.1.3.3 Optimizing Noise and PSRR
          1. 9.1.3.3.1 Charge Pump Noise
        4. 9.1.3.4 Load Transient Response
      4. 9.1.4 DC Performance
        1. 9.1.4.1 Output Voltage Accuracy (VOUT)
        2. 9.1.4.2 Dropout Voltage (VDO)
          1. 9.1.4.2.1 Behavior When Transitioning From Dropout Into Regulation
      5. 9.1.5 Sequencing Requirements
      6. 9.1.6 Negatively Biased Output
      7. 9.1.7 Reverse Current
      8. 9.1.8 Power Dissipation (PD)
        1. 9.1.8.1 Estimating Junction Temperature
        2. 9.1.8.2 Recommended Area for Continuous Operation (RACO)
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 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
        1. 12.1.1.1 Evaluation Models
        2. 12.1.1.2 Spice Models
      2. 12.1.2 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
  13. 13Mechanical, Packaging, and Orderable Information

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9.1.1.8 Noise-Reduction and Soft-Start Capacitor (CNR/SS)

The TPS7A83A features a programmable, monotonic, voltage-controlled soft-start that is set with an external capacitor (CNR/SS).The use of an external CNR/SS is highly recommended, especially to minimize in-rush current into the output capacitors. This soft-start eliminates power-up initialization problems when powering field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or other processors. The controlled voltage ramp of the output also reduces peak in-rush current during start up, minimizing start-up transients to the input power bus.

To achieve a monotonic start-up, the TPS7A83A error amplifier tracks the voltage ramp of the external soft-start capacitor until the voltage approaches the internal reference. The soft-start ramp time depends on the soft-start charging current (INR/SS), the soft-start capacitance (CNR/SS), and the internal reference (VNR/SS). Use Equation 6 to calculate the soft-start ramp time:

Equation 6. tSS = (VNR/SS × CNR/SS) / INR/SS

The noise-reduction capacitor, in conjunction with the noise-reduction resistor, forms a low-pass filter (LPF) that filters out the noise from the reference before being gained up with the error amplifier, thereby reducing the device noise floor. The LPF is a single-pole filter and Equation 7 to calculates the cutoff frequency. The typical value of RNR/SS is 250 kΩ. Increasing the CNR/SS capacitor has a greater affect because the output voltage increases when the noise from the reference is gained up even more at higher output voltages. For low-noise applications, a 10-nF to 1-µF CNR/SS is recommended. When a CNR/SS capacitor gets larger, the capacitor leakage increases, causing a longer than expected start-up time.

Equation 7. fcutoff = 1/ (2 × π × RNR/SS × CNR/SS)