ZHCS547K January 2010 – February 2018 LM27402
PRODUCTION DATA.
- 1 特性
- 2 應用
- 3 說明
- 4 修訂歷史記錄
- 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 Wide Input Voltage Range
- 7.3.2 UVLO
- 7.3.3 Precision Enable
- 7.3.4 Soft-Start and Voltage Tracking
- 7.3.5 Output Voltage Setpoint and Accuracy
- 7.3.6 Voltage-Mode Control
- 7.3.7 Power Good
- 7.3.8 Inductor-DCR-Based Overcurrent Protection
- 7.3.9 Current Sensing
- 7.3.10 Power MOSFET Gate Drivers
- 7.3.11 Pre-Bias Start-up
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1
Application Information
- 8.1.1 Converter Design
- 8.1.2 Inductor Selection (L)
- 8.1.3 Output Capacitor Selection (COUT)
- 8.1.4 Input Capacitor Selection (CIN)
- 8.1.5 Using Precision Enable
- 8.1.6 Setting the Soft-Start Time
- 8.1.7 Tracking
- 8.1.8 Setting the Switching Frequency
- 8.1.9 Setting the Current Limit Threshold
- 8.1.10 Control Loop Compensation
- 8.1.11 MOSFET Gate Drivers
- 8.1.12 Power Loss and Efficiency Calculations
- 8.2 Typical Applications
- 8.1
Application Information
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機械、封裝和可訂購信息
封裝選項
機械數據 (封裝 | 引腳)
散熱焊盤機械數據 (封裝 | 引腳)
訂購信息
8.1.5 Using Precision Enable
If enable (EN) is not controlled directly, the LM27402 can be pre-programmed to turn on at an input voltage higher than the UVLO voltage. This is done with an external resistor divider from VIN to EN and EN to GND as shown in Figure 28.
Figure 28. Enable Sequencing
The resistor values of RA and RB are relatively sized to allow the EN pin to reach the precision enable threshold voltage at the appropriate input supply voltage. With the enable current source considered, the equation to solve for RA is Equation 9:
where RA is the resistor from VIN to EN, RB is the resistor from EN to GND, IEN is the internal enable pull-up current (2 µA) and 1.17 V is the fixed precision enable threshold voltage. Typical values for RB range from 10 kΩ to 100 kΩ.