ZHCSD59F June 2012 – November 2017 LM34926
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 Design Requirements
- 8.2.2
Detailed Design Procedure
- 8.2.2.1 Custom Design With WEBENCH® Tools
- 8.2.2.2 Transformer Turns Ratio
- 8.2.2.3 Total IOUT
- 8.2.2.4 RFB1, RFB2
- 8.2.2.5 Frequency Selection
- 8.2.2.6 Transformer Selection
- 8.2.2.7 Primary Output Capacitor
- 8.2.2.8 Secondary Output Capacitor
- 8.2.2.9 Type III Feedback Ripple Circuit
- 8.2.2.10 Secondary Diode
- 8.2.2.11 VCC and Bootstrap Capacitor
- 8.2.2.12 Input Capacitor
- 8.2.2.13 UVLO Resistors
- 8.2.2.14 VCC Diode
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
7.3.5 On-Time Generator
The on-time for the LM34926 device is determined by the RON resistor, and is inversely proportional to the input voltage (VIN), resulting in a nearly constant frequency as VIN is varied over its range. The on-time equation for the LM34926 is determined be Equation 3.
Equation 3. 
See Figure 5. RON should be selected for a minimum on-time (at maximum VIN) greater than 100 ns, for proper operation. This requirement limits the maximum frequency for each application.