ZHCS360F July 2012 – November 2020 TPS54020
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Description (Continued)
- 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 Input Voltage and Power Input Voltage Pins (VIN and PVIN)
- 8.3.3 Voltage Reference (VREF)
- 8.3.4 Adjusting the Output Voltage
- 8.3.5 Safe Start-up into Prebiased Outputs
- 8.3.6 Error Amplifier
- 8.3.7 Slope Compensation
- 8.3.8 Enable and Adjusting Undervoltage Lockout
- 8.3.9 Adjustable Switching Frequency and Synchronization (RT/CLK)
- 8.3.10 Soft-Start (SS) Sequence
- 8.3.11 Power Good (PWRGD)
- 8.3.12 Bootstrap Voltage (BOOT) and Low Dropout Operation
- 8.3.13 Sequencing (SS)
- 8.3.14 Output Overvoltage Protection (OVP)
- 8.3.15 Overcurrent Protection
- 8.3.16 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 Operating Frequency
- 9.2.2.3 Output Inductor Selection
- 9.2.2.4 Output Capacitor Selection
- 9.2.2.5 Input Capacitor Selection
- 9.2.2.6 Soft-Start Capacitor Selection
- 9.2.2.7 Bootstrap Capacitor Selection
- 9.2.2.8 Undervoltage Lockout Set Point
- 9.2.2.9 Output Voltage Feedback Resistor Selection
- 9.2.2.10 Compensation Component Selection
- 9.2.3 Application Curves
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.10 Soft-Start (SS) Sequence
The device has two non-inverting inputs to the error amplifier. One input is the 0.6-V reference (VREF) , and the other is the SS pin voltage. The device regulates to the lower of these two voltages. A capacitor on the SS pin to ground implements a soft-start time. The internal pullup current source of 2.3 μA charges the external soft-start capacitor. The calculations for the soft-start time (tSS, 10% to 90%) and soft-start capacitor (CSS) are shown in Equation 4. The voltage reference (VREF) is 0.6 V and the soft-start charge current (ISS) is 2.3 μA.
where
- CSS is the soft-start capacitance in nF
- ISS is the soft-start current in μA
- tSS is the soft-start time in ms
- VREF of the voltage reference in V
The device stops switching and enters low-current operation when either the input voltage UVLO is triggered, the EN pin is pulled below 1.2 V, or if a thermal shutdown event occurs. During the subsequent power up sequence, when the shutdown condition is removed, the device does not start switching until it has discharged the SS pin to ground ensuring proper soft-start behavior.