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
7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
The switching frequency of the TPS54418 device is adjustable over a wide range from 200 kHz to 2000 kHz by placing a maximum of 1000 kΩ and minimum of 85 kΩ, respectively, on the RT/CLK pin. An internal amplifier holds this pin at a fixed voltage when using an external resistor to ground to set the switching frequency. The RT/CLK is typically 0.5 V. To determine the timing resistance for a given switching frequency, use the curve in Figure 5 or Figure 6 or Equation 5.
where
- RRT is in kΩ
- fSW is in kHz
where
- RRT is in kΩ
- fSW is in kHz
To reduce the solution size one would typically set the switching frequency as high as possible, but tradeoffs of the efficiency, maximum input voltage and minimum controllable on time should be considered.
The minimum controllable on time is typically 60 ns at full current load and 110 ns at no load, and limits the maximum operating input voltage or output voltage.