ZHCSD58G June 2012 – November 2017 LM34925
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Control Overview
- 7.3.2 VCC Regulator
- 7.3.3 Regulation Comparator
- 7.3.4 Overvoltage Comparator
- 7.3.5 On-Time Generator
- 7.3.6 Current Limit
- 7.3.7 N-Channel Buck Switch and Driver
- 7.3.8 Synchronous Rectifier
- 7.3.9 Undervoltage Detector
- 7.3.10 Thermal Protection
- 7.3.11 Ripple Configuration
- 7.3.12 Soft Start
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Application
- 8.2.1
Application Circuit: 20-V to 95-V Input and 10-V, 100-mA Output Isolated Fly-Buck Converter
- 8.2.1.1 Design Requirements
- 8.2.1.2
Detailed Design Procedure
- 8.2.1.2.1 Transformer Turns Ratio
- 8.2.1.2.2 Total IOUT
- 8.2.1.2.3 RFB1, RFB2
- 8.2.1.2.4 Frequency Selection
- 8.2.1.2.5 Transformer Selection
- 8.2.1.2.6 Primary Output Capacitor
- 8.2.1.2.7 Secondary Output Capacitor
- 8.2.1.2.8 Type III Feedback Ripple Circuit
- 8.2.1.2.9 Secondary Diode
- 8.2.1.2.10 VCC and Bootstrap Capacitor
- 8.2.1.2.11 Input Capacitor
- 8.2.1.2.12 UVLO Resistors
- 8.2.1.2.13 VCC Diode
- 8.2.2 Application Curves
- 8.2.1
Application Circuit: 20-V to 95-V Input and 10-V, 100-mA Output Isolated Fly-Buck Converter
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.2.1.2.12 UVLO Resistors
UVLO resistors RUV1 and RUV2 set the undervoltage lockout threshold and hysteresis according to Equation 19 and Equation 20.
Equation 19. 
Equation 20. 
Where IHYS = 20 μA, typical.
For a UVLO hysteresis of 2.5 V and UVLO rising threshold of 20 V, Equation 19 and Equation 20 require RUV1 of 8.25 kΩ and RUV2 of 127 kΩ and these values are selected for this design example.