JAJSHH0E August 2013 – May 2019 TPS54618-Q1
PRODUCTION DATA.
- 1 特長
- 2 アプリケーション
- 3 概要
- 4 改訂履歴
- 5 概要（続き）
- 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 PWM Control
- 8.3.2 Slope Compensation and Output Current
- 8.3.3 Bootstrap Voltage (Boot) and Low Dropout Operation
- 8.3.4 Error Amplifier
- 8.3.5 Voltage Reference
- 8.3.6 Adjusting the Output Voltage
- 8.3.7 Enable and Adjusting Undervoltage Lockout
- 8.3.8 Soft-Start Pin
- 8.3.9 Sequencing
- 8.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
- 8.3.11 Overcurrent Protection
- 8.3.12 Frequency Shift
- 8.3.13 Reverse Overcurrent Protection
- 8.3.14 Synchronize Using the RT/CLK Pin
- 8.3.15 Power Good (PWRGD Pin)
- 8.3.16 Overvoltage Transient Protection
- 8.3.17 Thermal Shutdown
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Custom Design With WEBENCH® Tools
- 9.2.2.2 Step One: Select the Switching Frequency
- 9.2.2.3 Step Two: Select the Output Inductor
- 9.2.2.4 Step Three: Choose the Output Capacitor
- 9.2.2.5 Step Four: Select the Input Capacitor
- 9.2.2.6 Step Five: Choose the Soft-Start Capacitor
- 9.2.2.7 Step Six: Select the Bootstrap Capacitor
- 9.2.2.8 Step Eight: Select Output Voltage and Feedback Resistors
- 9.2.2.9 Step Nine: Select Loop Compensation Components
- 9.2.3 Application Curves
- 10Power Supply Recommendations
- 11Layout
- 12デバイスおよびドキュメントのサポート
- 13メカニカル、パッケージ、および注文情報
9.2.2.3 Step Two: Select the Output Inductor
The inductor selected works for the entire TPS54618-Q1 input voltage range. To calculate the value of the output inductor, use Equation 22. 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 high inductor ripple currents 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. In general, the inductor ripple value is at the discretion of the designer; however, KIND is normally from 0.1 to 0.3 for the majority of applications.
For this design example, use KIND = 0.3 and the inductor value is calculated to be 0.7 μH. For this design, a nearest standard value was chosen: 0.75 μH. For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded. The RMS and peak inductor current can be found from Equation 24 and Equation 25.
For this design, the RMS inductor current is 6.01 A and the peak inductor current is 6.84 A. The chosen inductor is a Toko FDV0630-R75M. It has a saturation current rating of 10 A and a RMS current rating of 8.9 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.
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