JAJSLY1G July   2013  – June 2021 TPS54561

PRODUCTION DATA  

  1. 特長
  2. アプリケーション
  3. 概要
  4. Revision History
  5. Pin Configuration and Functions
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed Frequency PWM Control
      2. 7.3.2  Slope Compensation Output Current
      3. 7.3.3  Pulse Skip Eco-mode
      4. 7.3.4  Low Dropout Operation and Bootstrap Voltage (BOOT)
      5. 7.3.5  Error Amplifier
      6. 7.3.6  Adjusting the Output Voltage
      7. 7.3.7  Enable and Adjusting Undervoltage Lockout
      8. 7.3.8  Soft Start/Tracking Pin (SS/TR)
      9. 7.3.9  Sequencing
      10. 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK) Pin)
      11. 7.3.11 Maximum Switching Frequency
      12. 7.3.12 Synchronization to RT/CLK Pin
      13. 7.3.13 Accurate Current Limit Operation
      14. 7.3.14 Power Good (PWRGD Pin)
      15. 7.3.15 Overvoltage Protection
      16. 7.3.16 Thermal Shutdown
      17. 7.3.17 Small Signal Model for Loop Response
      18. 7.3.18 Simple Small Signal Model for Peak Current Mode Control
      19. 7.3.19 Small Signal Model for Frequency Compensation
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Buck Converter for 7-V to 60-V Input to 5-V at 5-A Output
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Custom Design with WEBENCH® Tools
          2. 8.2.1.2.2  Selecting the Switching Frequency
          3. 8.2.1.2.3  Output Inductor Selection (LO)
          4. 8.2.1.2.4  Output Capacitor
          5. 8.2.1.2.5  Catch Diode
          6. 8.2.1.2.6  Input Capacitor
          7. 8.2.1.2.7  Slow Start Capacitor
          8. 8.2.1.2.8  Bootstrap Capacitor Selection
          9. 8.2.1.2.9  Undervoltage Lockout Set Point
          10. 8.2.1.2.10 Output Voltage and Feedback Resistors Selection
          11. 8.2.1.2.11 Compensation
          12. 8.2.1.2.12 Power Dissipation Estimate
          13. 8.2.1.2.13 Safe Operating Area
          14. 8.2.1.2.14 Discontinuous Conduction Mode and Eco-mode Boundary
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Inverting Buck-Boost Topology for Positive Input to Negative Output
      3. 8.2.3 Split-Rail Topology for Positive Input to Negative and Positive Output
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Estimated Circuit Area
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design with WEBENCH® Tools
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 サポート・リソース
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

Synchronization to RT/CLK Pin

The RT/CLK pin can receive a frequency synchronization signal from an external system clock. To implement this synchronization feature connect a square wave to the RT/CLK pin through either circuit network shown in Figure 7-12. The square wave applied to the RT/CLK pin must switch lower than 0.5 V and higher than 2 V and have a pulse width greater than 15 ns. The synchronization frequency range is 160 kHz to 2300 kHz. The rising edge of the SW will be synchronized to the falling edge of RT/CLK pin signal. The external synchronization circuit should be designed such that the default frequency set resistor is connected from the RT/CLK pin to ground when the synchronization signal is off. When using a low impedance signal source, the frequency set resistor is connected in parallel with an ac coupling capacitor to a termination resistor (that is, 50 Ω) as shown in Figure 7-12. The two resistors in series provide the default frequency setting resistance when the signal source is turned off. The sum of the resistance should set the switching frequency close to the external CLK frequency. AC coupling the synchronization signal through a 10-pF ceramic capacitor to RT/CLK pin is recommended.

The first time the RT/CLK is pulled above the PLL threshold the TPS54561 switches from the RT resistor free-running frequency mode to the PLL synchronized mode. The internal 0.5 V voltage source is removed and the RT/CLK pin becomes high impedance as the PLL starts to lock onto the external signal. The switching frequency can be higher or lower than the frequency set with the RT/CLK resistor. The device transitions from the resistor mode to the PLL mode and locks onto the external clock frequency within 78 microseconds. During the transition from the PLL mode to the resistor programmed mode, the switching frequency will fall to 150 kHz and then increase or decrease to the resistor programmed frequency when the 0.5-V bias voltage is reapplied to the RT/CLK resistor.

The switching frequency is divided by 8, 4, 2, and 1 as the FB pin voltage ramps from 0 to 0.8 V. The device implements a digital frequency foldback to enable synchronizing to an external clock during normal start-up and fault conditions. Figure 7-13, Figure 7-14, and Figure 7-15 show the device synchronized to an external system clock in continuous conduction mode (CCM), discontinuous conduction (DCM), and pulse skip mode (Eco-Mode).

GUID-DE9E88EC-A598-4A4E-B4EF-F2A7E42E6168-low.gifFigure 7-12 Synchronizing to a System Clock
GUID-EE6AD695-2F77-4F8A-BED0-BD4D7D9D73AA-low.gifFigure 7-13 Plot of Synchronizing in CCM
GUID-D5DFFA55-0F27-4621-8EEB-5EB2919B3F3F-low.gifFigure 7-15 Plot of Synchronizing in Eco-mode
GUID-7AFA6108-07C4-4E7B-8257-0DEFC89EC82F-low.gifFigure 7-14 Plot of Synchronizing in DCM