ZHCSFE2A August   2016  – November 2017 LM5161-Q1

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      典型降压应用电路
      2.      典型 Fly-Buck 应用电路
  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 Switching Characteristics
    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  Control Circuit
      2. 7.3.2  VCC Regulator
      3. 7.3.3  Regulation Comparator
      4. 7.3.4  Soft-Start
      5. 7.3.5  Error Transconductance (GM) Amplifier
      6. 7.3.6  On-Time Generator
      7. 7.3.7  Current Limit
      8. 7.3.8  N-Channel Buck Switch and Driver
      9. 7.3.9  Synchronous Rectifier
      10. 7.3.10 Enable / Undervoltage Lockout (EN/UVLO)
      11. 7.3.11 Thermal Protection
      12. 7.3.12 Ripple Configuration
    4. 7.4 Device Functional Modes
      1. 7.4.1 Forced Pulse Width Modulation (FPWM) Mode
      2. 7.4.2 Undervoltage Detector
  8. 8 Applications and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 LM5161-Q1 Synchronous Buck (15-V to 95-V Input, 12-V Output, 1-A Load)
        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  Output Resistor Divider Selection
          3. 8.2.1.2.3  Frequency Selection
          4. 8.2.1.2.4  Inductor Selection
          5. 8.2.1.2.5  Output Capacitor Selection
          6. 8.2.1.2.6  Series Ripple Resistor - RESR (FPWM = 1)
          7. 8.2.1.2.7  VCC and Bootstrap Capacitor
          8. 8.2.1.2.8  Input Capacitor Selection
          9. 8.2.1.2.9  Soft-Start Capacitor Selection
          10. 8.2.1.2.10 EN/UVLO Resistor Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 LM5161-Q1 Isolated Fly-Buck (36-V to 72-V Input, 12-V, 12-W Isolated Output)
        1. 8.2.2.1 LM5161-Q1 Fly-Buck Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Selection of VOUT and Turns Ratio
          2. 8.2.2.2.2 Secondary Rectifier Diode
          3. 8.2.2.2.3 External Ripple Circuit
          4. 8.2.2.2.4 Output Capacitor (CVISO)
        3. 8.2.2.3 Application Curves
    3. 8.3 Do's and Don'ts
  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 器件支持
      1. 11.1.1 开发支持
        1. 11.1.1.1 使用 WEBENCH® 工具创建定制设计
    2. 11.2 相关文档
    3. 11.3 商标
    4. 11.4 接收文档更新通知
    5. 11.5 社区资源
    6. 11.6 静电放电警告
    7. 11.7 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

7.4.1 Forced Pulse Width Modulation (FPWM) Mode

The Synchronous Rectifier section gives a brief introduction to the LM5161-Q1 diode emulation feature. The FPWM pin allows the power supply designer to select either CCM or DCM mode of operation at light loads. When the FPWM pin is connected to ground or left floating (FPWM = 0), a pulse-skipping mode and the zero-cross current detector circuit is enabled. The zero-cross detector turns off the low-side FET when the inductor current falls close to zero (IZX, seeElectrical Characteristics). This feature allows the LM5161-Q1 regulator to operate in DCM mode at light loads. In the DCM state, the switching frequency decreases with lighter loads.

When the FPWM pin is left open or shorted to ground, the user can take the advantage of the internal ripple injection circuit, enabled in this mode, for a typical Buck application circuit. This feature is applicable over the entire load and input voltage ranges. It eliminates the need for an external feedback ripple injection circuit.

For wide VIN applications where VIN > 72 V, an external VCC supply is commonly used to minimize the power dissipation in the IC. In such applications at TJ>125°C, it is recommended to add a BST resistor (> 3Ω) in series with the BST capacitor, in order to protect the internal VCC-BST diode during a full load transient operation. The addition of the external resistor will reduce the fast (dv/dt) of the switch node that can impact the normal IC operation.

If the FPWM pin is pulled high, the LM5161-Q1 will operate in CCM mode regardless of the load conditions. The CCM operation reduces efficiency at light load but improves the output transient response to step load changes and provides nearly constant switching frequency. Moreover, the Fly-Buck topology always requires the continuous conduction mode during its operation.

The internal ripple injection circuit is disabled in the CCM mode. An external ripple injection circuit or an additional ESR resistor in series with the output capacitor is required to generate the optimal ripple at the FB node. Also, there is no need to add any BST resistor in series with the BST capacitor in either forced CCM Buck or Fly-Buck application.

Table 2. FPWM Pin Mode Summary

FPWM PIN CONNECTION LOGIC STAGE DESCRIPTION
GND or Floating (High Z) 0 The FPWM pin is grounded or left floating. DCM enabled at light loads. Internal Ripple circuit is enabled. No external ripple circuit/ addition required.
VCC 1 The FPWM pin is connected to VCC. The LM5161-Q1 then operates in CCM mode at light loads. Internal ripple injection disabled. External ripple injection needed.
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