ZHCSI03C September 2009 – April 2018 TPS54318
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
8.2.2.9.1 Output Voltage Limitations
Due to the internal design of the TPS54318, there are limitations to the minimum and maximum achievable output voltages. The output voltage can never be lower than the internal voltage reference of 0.8 V. Above 0.8 V, the output voltage may be limited by the minimum controllable on time. The minimum output voltage in this case is given by Equation 35. There is also a maximum achievable output voltage which is limited by the minimum off time. The maximum output voltage is given by Equation 36. These equations represent the results when the power MOSFETs are matched. Refer to SLYT293 for more information.
Equation 35. 
where
- VOUT(min) is the minimum achievable output voltage
- tON(min) is the minimum controllable on-time (110 nsec typical)
- fSW(max) is the maximum switching frequency including tolerance
- VIN(max) is the maximum input voltage
- IOUT(min) is the minimum load current
- RLS(min) is the minimum low-side MOSFET on-resistance. (30 mΩ typical)
- RDCR is the series resistance of output inductor
Equation 36. 
where
- VOUT(max) is the maximum achievable output voltage
- tOFF(max) is the maximum, minimum controllable off time (60 ns typical)
- fSW(max) is the maximum switching frequency including tolerance
- VIN(min) is the minimum input voltage
- IOUT(max) is the maximum load current
- RHS(max) is the maximum high-side MOSFET on-resistance. (70 mΩ max)
- RDCR is the series resistance of output inductor