ZHCSI04E September 2009 – April 2018 TPS54418
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 Slope Compensation and Output Current
- 7.3.3 Bootstrap Voltage (Boot) and Low Dropout Operation
- 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
- 7.3.8 Soft-Start Pin
- 7.3.9 Sequencing
- 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
- 7.3.11 Overcurrent Protection
- 7.3.12 Frequency Shift
- 7.3.13 Reverse Overcurrent Protection
- 7.3.14 Synchronize Using the RT/CLK Pin
- 7.3.15 Power Good (PWRGD Pin)
- 7.3.16 Overvoltage Transient Protection
- 7.3.17 Thermal Shutdown
- 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 Step One: Select the Switching Frequency
- 8.2.2.2 Step Two: Select the Output Inductor
- 8.2.2.3 Step Three: Choose the Output Capacitor
- 8.2.2.4 Step Four: Select the Input Capacitor
- 8.2.2.5 Step Five: Minimum Load DC COMP Voltage
- 8.2.2.6 Step Six: Choose the Soft-Start Capacitor
- 8.2.2.7 Step Seven: Select the Bootstrap Capacitor
- 8.2.2.8 Step Eight: Undervoltage Lockout Threshold
- 8.2.2.9 Step Nine: Select Output Voltage and Feedback Resistors
- 8.2.2.10 Step 10: Select Loop Compensation Components
- 8.2.2.11 Power Dissipation Estimate
- 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
7.3.8 Soft-Start Pin
The TPS54418 device regulates to the lower of the SS pin and the internal reference voltage. A capacitor on the SS pin to ground implements a soft-start time. The TPS54418 device has an internal pull-up current source of 1.8 μA which charges the external soft-start capacitor. Equation 4 calculates the required soft-start capacitor value where tSS is the desired soft-start time in ms, ISS is the internal soft-start charging current of 1.8 μA, and VREF is the internal voltage reference of 0.8 V. it is recommended to maintain the soft-start time in the range between 1 ms and 10 ms.
where
- CSS is in nF
- tSS is in ms
- ISS is in µA
- VREF is in V
If during normal operation, the input voltage goes below the UVLO, EN pin pulled below 1.2 V, or a thermal shutdown event occurs, the TPS54418 device stops switching and the SS is discharged to 0 volts before reinitiating a powering up sequence.