ZHCS573I August 2010 – April 2018 LM25119
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 High Voltage Start-Up Regulator
- 7.3.2 UVLO
- 7.3.3 Enable 2
- 7.3.4 Oscillator and Sync Capability
- 7.3.5 Error Amplifiers and PWM Comparators
- 7.3.6 Ramp Generator
- 7.3.7 Current Limit
- 7.3.8 Hiccup Mode Current Limiting
- 7.3.9 Soft Start
- 7.3.10 HO and LO Output Drivers
- 7.3.11 Maximum Duty Cycle
- 7.3.12 Thermal Protection
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
Dual-output Design Example
- 8.2.1.1 Design Requirements
- 8.2.1.2
Detailed Design Procedure
- 8.2.1.2.1 Timing Resistor
- 8.2.1.2.2 Output Inductor
- 8.2.1.2.3 Current Sense Resistor
- 8.2.1.2.4 Ramp Resistor and Ramp Capacitor
- 8.2.1.2.5 Output Capacitors
- 8.2.1.2.6 Input Capacitors
- 8.2.1.2.7 VCC Capacitor
- 8.2.1.2.8 Bootstrap Capacitor
- 8.2.1.2.9 Soft Start Capacitor
- 8.2.1.2.10 Restart Capacitor
- 8.2.1.2.11 Output Voltage Divider
- 8.2.1.2.12 UVLO Divider
- 8.2.1.2.13 MOSFET Selection
- 8.2.1.2.14 MOSFET Snubber
- 8.2.1.2.15 Error Amplifier Compensation
- 8.2.1.3 Application Curves
- 8.2.2 Two-Phase Design Example
- 8.2.1
Dual-output Design Example
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.2.1.2.1 Timing Resistor
RT sets the switching frequency of each regulator channel. Generally, higher frequency applications are smaller but have higher losses. Operation at 230 kHz was selected for this example as a reasonable compromise between small size and high efficiency. The value of RT for 230-kHz switching frequency is calculated with Equation 7.
Equation 7. 
A standard value or 22.1 kΩ was chosen for RT. The internal oscillator frequency is twice the switching frequency and is about 460 kHz.