ZHCSI26C August 2010 – April 2018 TPS54320
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 Fixed Frequency PWM Control
- 7.3.2 Continuous Current Mode Operation (CCM)
- 7.3.3 VIN and Power VIN Pins (VIN and PVIN)
- 7.3.4 Voltage Reference
- 7.3.5 Adjusting the Output Voltage
- 7.3.6 Safe Start-up into Prebiased Outputs
- 7.3.7 Error Amplifier
- 7.3.8 Slope Compensation
- 7.3.9 Enable and Adjusting UVLO
- 7.3.10 Slow Start (SS/TR)
- 7.3.11 Power Good (PWRGD)
- 7.3.12 Bootstrap Voltage (BOOT) and Low Dropout Operation
- 7.3.13 Sequencing (SS/TR)
- 7.3.14 Output Overvoltage Protection (OVP)
- 7.3.15 Overcurrent Protection
- 7.3.16 Thermal Shutdown
- 7.3.17 Small Signal Model for Loop Response
- 7.3.18 Simple Small Signal Model for Peak Current Mode Control
- 7.3.19 Small Signal Model for Frequency Compensation
- 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 Operating Frequency
- 8.2.2.3 Output Inductor Selection
- 8.2.2.4 Output Capacitor Selection
- 8.2.2.5 Input Capacitor Selection
- 8.2.2.6 Slow-Start Capacitor Selection
- 8.2.2.7 Bootstrap Capacitor Selection
- 8.2.2.8 UVLO Set Point
- 8.2.2.9 Output Voltage Feedback Resistor Selection
- 8.2.2.10 Compensation Component Selection
- 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
8.2.2.3 Output Inductor Selection
To calculate the value of the output inductor, Equation 18 is used. KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing a high inductor ripple current impacts the selection of the output capacitor because the output capacitor must have a ripple current rating equal to or greater than the inductor ripple current. Usually, the inductor ripple value is at the discretion of the designer; however, KIND is normally from 0.2 to 0.4 for the majority of applications.
For this design example using KIND = 0.3, the inductor value is calculated to be 6.2 µH. The nearest standard value of 6.8 µH was chosen. For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded. The inductor ripple current, RMS current, and peak inductor current can be found from Equation 19, Equation 20, and Equation 21.
For this design, the inductor ripple current is 815 mA, the RMS inductor current is 3.01 A, and the peak inductor current is 3.41 A. A 6.8-µH TDK VLP8040 series inductor was chosen for its small size and low DCR. It has a saturation current rating of 3.6 A and a RMS current rating of 4 A.
The current flowing through the inductor is the inductor ripple current plus the output current. During power up, faults or transient load conditions, the inductor current can increase above the calculated peak inductor current level calculated above. In transient conditions, the inductor current can increase up to the switch current limit of the device. For this reason, the most conservative approach is to specify an inductor with a saturation current rating equal to or greater than the switch current limit rather than the peak inductor current.