JAJU823 August   2021

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
    4. 2.4 System Design Theory
      1. 2.4.1 Buck Converter Circuit Design Using TPS62903
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Startup
      2. 3.3.2 Load Transient
      3. 3.3.3 Output Ripple
      4. 3.3.4 Efficiency
      5. 3.3.5 Thermal Performance
      6. 3.3.6 Output Voltage vs. Output Current
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 PCB Layout Recommendations
        1. 4.1.3.1 Layout Prints
      4. 4.1.4 Altium Project
      5. 4.1.5 Gerber Files
      6. 4.1.6 Assembly Drawings
    2. 4.2 Documentation Support
    3. 4.3 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

2.2 Design Considerations

By connecting 26.1-kΩ resistor on Mode/S-CONF pin, the device is configured to:

  • VSET-operation: VOUT is sensed only through the VOS pin by an internal resistor divider. The target Vout is programmed by an external resistor connected between the VSET pin and GND. In this design, FB/VSET is connected to GND and thus the VOUT is programmed to 1.2-V.
  • 2.5-MHz Switching Frequency with AEE (Automatic Efficiency Enhancement): The MODE/S-CONF pin is configured for AEE mode, the TPS62903 provides the highest efficiency over the entire input voltage and output voltage range by automatically adjusting the switching frequency of the converter. The efficiency decreases if VOUT decreases, VIN increases, or both. To keep the efficiency high over the entire duty cycle range (VOUT/VIN ratio), the switching frequency is adjusted while maintaining the ripple current. The AEE feature provides an efficiency enhancement for various duty cycles, especially for lower VOUT values where fixed frequency converters suffer from a significant efficiency drop. Furthermore, this feature compensates for the very small duty cycles of high VIN to low VOUT conversion, which limits the control range in other topologies.
  • Power Save Mode Operation (Auto PFM/PWM): The MODE/S-CONF pin is configured for power save mode (auto PFM/PWM). The device operates in PWM mode as long the output current is higher than half of the ripple current of the inductor. To maintain high efficiency at light loads, the device enters power save mode at the boundary to discontinuous conduction mode (DCM). This happens if the output current becomes smaller than half of the ripple current of the inductor. The power save mode is entered seamlessly when the load current decreases. This ensures a high efficiency in light load operation. The device remains in power save mode as long as the inductor current is discontinuous. In power save mode, the switching frequency decreases linearly with the load current maintaining high efficiency. The transition in and out of power save mode is seamless in both directions.
  • Output Discharge Function Enabled: The discharge function is enabled to ensure a defined down-ramp of the output voltage when the device is being disabled but also to keep the output voltage close to 0-V when the device is off. The output discharge feature is only active once TPS62903 has been enabled at least once since the supply voltage was applied.
  • Soft Start: The SS/TR pin left floating for fastest start up time.