ZHCSJ42 December   2018 TPS54340B

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化原理图
      2.      效率与负载电流间的关系
  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  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  Internal Soft Start
      9. 7.3.9  Constant Switching Frequency and Timing Resistor (RT/CLK) pin)
      10. 7.3.10 Accurate Current Limit Operation and Maximum Switching Frequency
      11. 7.3.11 Synchronization to RT/CLK pin
      12. 7.3.12 Overvoltage Protection
      13. 7.3.13 Thermal Shutdown
      14. 7.3.14 Small Signal Model for Loop Response
      15. 7.3.15 Simple Small Signal Model for Peak-Current-Mode Control
      16. 7.3.16 Small Signal Model for Frequency Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation with VIN ≤ 4.5 V (Minimum VIN)
      2. 7.4.2 Operation with EN Control
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application: Buck Converter
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedures
        1. 8.2.2.1  Custom Design with WEBENCH® Tools
        2. 8.2.2.2  Selecting the Switching Frequency
        3. 8.2.2.3  Output Inductor Selection (LO)
        4. 8.2.2.4  Output Capacitor
        5. 8.2.2.5  Catch Diode
        6. 8.2.2.6  Input Capacitor
        7. 8.2.2.7  Bootstrap Capacitor Selection
        8. 8.2.2.8  Undervoltage Lockout Setpoint
        9. 8.2.2.9  Output Voltage and Feedback Resistors Selection
        10. 8.2.2.10 Minimum VIN
        11. 8.2.2.11 Compensation
        12. 8.2.2.12 Discontinuous Conduction Mode and Eco-mode Boundary
        13. 8.2.2.13 Power Dissipation
      3. 8.2.3 Application Curves
    3. 8.3 Other Applications
      1. 8.3.1 Inverting Power
      2. 8.3.2 Split-Rail Power Supply
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
      1. 10.2.1 Estimated Circuit Area
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 第三方产品免责声明
      2. 11.1.2 使用 WEBENCH® 工具定制设计方案
    2. 11.2 接收文档更新通知
    3. 11.3 社区资源
    4. 11.4 商标
    5. 11.5 静电放电警告
  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

8.2.2.6 Input Capacitor

The TPS54340B requires a high quality ceramic type X5R or X7R input decoupling capacitor with at least 3 μF of effective capacitance. Some applications will benefit from additional bulk capacitance. The effective capacitance includes any loss of capacitance due to DC bias effects. The voltage rating of the input capacitor must be greater than the maximum input voltage. The capacitor must also have a ripple current rating greater than the maximum input current ripple of the TPS54340. The input ripple current can be calculated using Equation 38.

The value of a ceramic capacitor varies significantly with temperature and the DC bias applied to the capacitor. The capacitance variations due to temperature can be minimized by selecting a dielectric material that is more stable over temperature. X5R and X7R ceramic dielectrics are usually selected for switching regulator capacitors because they have a high capacitance to volume ratio and are fairly stable over temperature. The input capacitor must also be selected with consideration for the DC bias. The effective value of a capacitor decreases as the DC bias across a capacitor increases.

For this example design, a ceramic capacitor with at least a 42 V voltage rating is required to support the maximum input voltage. Common standard ceramic capacitor voltage ratings include 4 V, 6.3 V, 10 V, 16 V, 25 V, 50 V, or 100 V. For this example, two 2.2-μF, 100-V capacitors in parallel are used. Table 2 shows several choices of high voltage capacitors.

The input capacitance value determines the input ripple voltage of the regulator. The input voltage ripple can be calculated using Equation 39. Using the design example values, IOUT = 3.5 A, CIN = 4.4 μF, ƒsw = 600 kHz, yields an input voltage ripple of 331 mV and a rms input ripple current of 1.74 A.

Equation 38. TPS54340B q_Ic_rms_lvsBK0.gif
Equation 39. TPS54340B q_deltavin_lvsbb4.gif

Table 2. Capacitor Types

VALUE (μF) EIA Size VOLTAGE DIALECTRIC COMMENTS
1 to 2.2 1210 100 V X7R GRM32 series
1 to 4.7 50 V
1 1206 100 V GRM31 series
1 to 2.2 50 V
1 to 1.8 2220 50 V VJ X7R series
1 to 1.2 100 V
1 to 3.9 2225 50 V
1 to 1.8 100 V
1 to 2.2 1812 100 V C series C4532
1.5 to 6.8 50 V
1 to 2.2 1210 100 V C series C3225
1 to 3.3 50 V
1 to 4.7 1210 50 V X7R dielectric series
1 100 V
1 to 4.7 1812 50 V
1 to 2.2 100 V