ZHCSJ24A November   2018  – May 2019 TPS56339

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化原理图
      2.      TPS56339 效率
  4. 4 修订历史记录
  5. 5 Pin Configuration and Functions
    1.     Pin 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
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Advanced Emulated Current Mode Control
      2. 7.3.2 Enable and Adjusting Undervoltage Lockout
      3. 7.3.3 Soft Start and Pre-Biased Soft Start
      4. 7.3.4 Voltage Reference
      5. 7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Dropout Conditions
      6. 7.3.6 Overcurrent and Undervoltage Protection
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Operation
    5. 7.5 Light-Load Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Resistors Selection
        3. 8.2.2.3 Output Inductor Selection
        4. 8.2.2.4 Output Capacitor Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Bootstrap Capacitor Selection
      3. 8.2.3 Undervoltage Lockout Set Point
      4. 8.2.4 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 接收文档更新通知
    2. 11.2 相关链接
    3. 11.3 社区资源
    4. 11.4 商标
    5. 11.5 静电放电警告
    6. 11.6 Glossary
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Dropout Conditions

Minimum ON-time, TON_MIN, is the smallest duration of time that the high-side MOSFET can be on. TON_MIN is typically 55ns in the TPS56339. Minimum OFF-time, TOFF_MIN, is the smallest duration that the high-side MOSFET can be off. TOFF_MIN is typically 115 ns in the TPS56339. In CCM operation, TON_MIN and TOFF_MIN  limit the voltage conversion range given a fixed switching frequency.

The minimum duty cycle allowed is:

Equation 4. DMIN = TON_MIN × fSW

And the maximum duty cycle allowed is:

Equation 5. DMAX = 1 – TOFF_MIN × fSW

In the TPS56339, a frequency foldback scheme is employed to extend the maximum duty cycle when TOFF_MIN is reached. The switching frequency decreases once longer duty cycle is needed under low VIN conditions. With the duty increase, the on time will increase, until up to the Maximum ON-time, 5 μs. Wide range of frequency foldback allows the TPS56339 output voltage stay in regulation with a much lower supply voltage VIN. This leads to a lower effective dropout voltage.

Given an output voltage, the maximum operation supply voltage can be found by:

Equation 6. TPS56339 eq-07-SLVSEI2.gif

At lower supply voltage, the switching frequency decreases once TOFF_MIN is triggered. The minimum VIN without frequency foldback can be approximated by:

Equation 7. TPS56339 eq-08-SLVSEI2.gif

Taking considerations of power losses in the system with heavy load operation, VIN_MAX is higher than the result calculated in Equation 6. With frequency foldback, VIN_MIN is lowered by decreased fSW, as shown in Figure 16 .

TPS56339 FrequencyFoldback_SLVSEI2.gifFigure 16. Frequency Foldback at Dropout (VOUT = 5 V)