ZHCS026C December 2010 – February 2016 TPS57060-Q1
PRODUCTION DATA.
- 1 特征
- 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 Slope Compensation Output Current
- 7.3.3 Low Dropout Operation and Bootstrap Voltage (BOOT)
- 7.3.4 Error Amplifier
- 7.3.5 Voltage Reference
- 7.3.6 Adjusting the Output Voltage
- 7.3.7 Enable and Adjusting Undervoltage Lockout (UVLO)
- 7.3.8 Slow Start and Tracking Pin (SS/TR)
- 7.3.9 Overload Recovery Circuit
- 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
- 7.3.11 Overcurrent Protection and Frequency Shift
- 7.3.12 Selecting the Switching Frequency
- 7.3.13 How to Interface to RT/CLK Pin
- 7.3.14 Power Good (PWRGD Pin)
- 7.3.15 Overvoltage Transient 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 Selecting the Switching Frequency
- 8.2.2.2 Output Inductor Selection (LO)
- 8.2.2.3 Output Capacitor
- 8.2.2.4 Catch Diode
- 8.2.2.5 Input Capacitor
- 8.2.2.6 Slow Start Capacitor
- 8.2.2.7 Bootstrap Capacitor Selection
- 8.2.2.8 Undervoltage Lockout Set Point
- 8.2.2.9 Output Voltage and Feedback Resistors Selection
- 8.2.2.10 Compensation
- 8.2.2.11 Discontinuous Mode and Eco Mode Boundary
- 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
封装选项
机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息
8.2.2.2 Output Inductor Selection (LO)
To calculate the minimum value of the output inductor, use Equation 28.
KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current.
The inductor ripple current will be filtered by the output capacitor. Therefore, choosing high inductor ripple currents will impact 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, the following guidelines may be used.
For designs using low ESR output capacitors such as ceramics, a value as high as KIND = 0.3 may be used. When using higher ESR output capacitors, KIND = 0.2 yields better results. Because the inductor ripple current is part of the PWM control system, the inductor ripple current should always be greater than 30 mA for dependable operation. In a wide input voltage regulator, it is best to choose an inductor ripple current on the larger side. This allows the inductor to still have a measurable ripple current with the input voltage at its minimum.
For this design example, use KIND = 0.3 and the minimum inductor value is calculated to be 39.7 μH. For this design, a nearest standard value was chosen: 47 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 30 and Equation 31.
For this design, the RMS inductor current is 0.501 A and the peak inductor current is 0.563 A. The chosen inductor is a MSS1048-473ML. It has a saturation current rating of 1.44 A and an RMS current rating of 1.83A.
As the equation set demonstrates, lower ripple currents will reduce the output voltage ripple of the regulator but will require a larger value of inductance. Selecting higher ripple currents will increase the output voltage ripple of the regulator but allow for a lower inductance value.
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.
