ZHCSL47A April 2020 – January 2021 LM5181
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Description (continued)
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 Integrated Power MOSFET
- 8.3.2 PSR Flyback Modes of Operation
- 8.3.3 Setting the Output Voltage
- 8.3.4 Control Loop Error Amplifier
- 8.3.5 Precision Enable
- 8.3.6 Configurable Soft Start
- 8.3.7 External Bias Supply
- 8.3.8 Minimum On-Time and Off-Time
- 8.3.9 Overcurrent Protection
- 8.3.10 Thermal Shutdown
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Applications
- 9.2.1
Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 5 V, 0.5 A
- 9.2.1.1 Design Requirements
- 9.2.1.2
Detailed Design Procedure
- 9.2.1.2.1 Custom Design With WEBENCH® Tools
- 9.2.1.2.2 Custom Design With Excel Quickstart Tool
- 9.2.1.2.3 Flyback Transformer – T1
- 9.2.1.2.4 Flyback Diode – DFLY
- 9.2.1.2.5 Zener Clamp Circuit – DF, DCLAMP
- 9.2.1.2.6 Output Capacitor – COUT
- 9.2.1.2.7 Input Capacitor – CIN
- 9.2.1.2.8 Feedback Resistor – RFB
- 9.2.1.2.9 Thermal Compensation Resistor – RTC
- 9.2.1.2.10 UVLO Resistors – RUV1, RUV2
- 9.2.1.2.11 Soft-Start Capacitor – CSS
- 9.2.2 Application Curves
- 9.2.1
Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 5 V, 0.5 A
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.3.1 Diode Thermal Compensation
The LM5181 employs a unique thermal compensation circuit that adjusts the feedback setpoint based on the thermal coefficient of the forward voltage drop of the flyback diode. Even though the output voltage is measured when the secondary current is effectively zero, there is still a non-zero forward voltage drop associated with the flyback diode. Select the thermal compensation resistor using Equation 9.
Equation 9. 
The temperature coefficient of the diode voltage drop may not be explicitly provided in the diode data sheet, so the effective value can be estimated based on the measured output voltage shift overtemperature when the TC resistor is not installed.