ZHCSCW5B August 2014 – September 2017 LM43600
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 简化电路原理图
- 5 修订历史记录
- 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 Fixed Frequency Peak Current Mode Controlled Step-Down Regulator
- 8.3.2 Light Load Operation
- 8.3.3 Adjustable Output Voltage
- 8.3.4 Enable (ENABLE)
- 8.3.5 VCC, UVLO and BIAS
- 8.3.6 Soft Start and Voltage Tracking (SS/TRK)
- 8.3.7 Switching Frequency (RT) and Synchronization (SYNC)
- 8.3.8 Minimum ON-Time, Minimum OFF-Time and Frequency Foldback at Dropout Conditions
- 8.3.9 Internal Compensation and CFF
- 8.3.10 Bootstrap Voltage (BOOT)
- 8.3.11 Power Good (PGOOD)
- 8.3.12 Overcurrent and Short-Circuit Protection
- 8.3.13 Thermal Shutdown
- 8.4 Device Functional Modes
-
9 Applications and Implementation
- 9.1 Application Information
- 9.2
Typical Applications
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Custom Design With WEBENCH® Tools
- 9.2.2.2 Output Voltage Setpoint
- 9.2.2.3 Switching Frequency
- 9.2.2.4 Input Capacitors
- 9.2.2.5 Inductor Selection
- 9.2.2.6 Output Capacitor Selection
- 9.2.2.7 Feedforward Capacitor
- 9.2.2.8 Bootstrap Capacitors
- 9.2.2.9 VCC Capacitor
- 9.2.2.10 BIAS Capacitors
- 9.2.2.11 Soft-Start Capacitors
- 9.2.2.12 Undervoltage Lockout Setpoint
- 9.2.2.13 PGOOD
- 9.2.3 Application Performance Curves
- 10Power Supply Recommendations
- 11Layout
- 12器件和文档支持
- 13机械、封装和可订购信息
封装选项
请参考 PDF 数据表获取器件具体的封装图。
机械数据 (封装 | 引脚)
- PWP|16
散热焊盘机械数据 (封装 | 引脚)
- PWP|16
订购信息
9.2.2.7 Feedforward Capacitor
The LM43600 is internally compensated and the internal R-C values are 400 kΩ and 50 pF, respectively. Depending on the VOUT and frequency FS, if the output capacitor COUT is dominated by low ESR (ceramic types) capacitors, it could result in low phase margin. To improve the phase boost an external feedforward capacitor CFF can be added in parallel with RFBT. CFF is chosen such that phase margin is boosted at the crossover frequency without CFF. A simple estimation for the crossover frequency without CFF (fx) is shown in Equation 21, assuming COUT has very small ESR.
The following equation for CFF was tested:
Equation 22 indicates that the crossover frequency is geometrically centered on the zero and pole frequencies caused by the CFF capacitor.
For designs with higher ESR, CFF is not neeed when COUT has very high ESR and CFF calculated from Equation 22 should be reduced with medium ESR. Table 2 can be used as a quick starting point.
For the application in this design example, a 33-pF COG capacitor is selected.