ZHCSAL1F November 2010 – May 2019 TPS54618
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 Custom Design With WEBENCH® Tools
- 8.2.2.2 Step One: Select the Switching Frequency
- 8.2.2.3 Step Two: Select the Output Inductor
- 8.2.2.4 Step Three: Choose the Output Capacitor
- 8.2.2.5 Step Four: Select the Input Capacitor
- 8.2.2.6 Step Five: Choose the Soft-Start Capacitor
- 8.2.2.7 Step Six: Select the Bootstrap Capacitor
- 8.2.2.8 Step Eight: Select Output Voltage and Feedback Resistors
- 8.2.2.9 Step Nine: Select Loop Compensation Components
- 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
8.2.2.8.1 Output Voltage Limitations
Due to the internal design of the TPS54618, there is a minimum output voltage limit for any given input voltage. The output voltage can never be lower than the internal voltage reference of 0.799 V. Above 0.799 V, the output voltage may be limited by the minimum controllable ON-time. The minimum output voltage in this case is given by Equation 34.
Equation 34. 
where
- Voutmin = minimum achievable output voltage
- Ontimemin = minimum controllable ON-time (75 ns typical. 120 ns no load)
- Fsmax = maximum switching frequency including tolerance
- Vinmax = maximum input voltage
- Ioutmin = minimum load current
- RDSmin = minimum high-side MOSFET ON-resistance (see Electrical Characteristics)
- RL = series resistance of output inductor
There is also a maximum achievable output voltage which is limited by the minimum OFF-time. The maximum output voltage is given by Equation 35.
Equation 35. 
where
- Voutmax = maximum achievable output voltage
- Vin = minimum input voltage
- Offtimemax = maximum OFF-time (90 ns typical for adequate margin)
- ts = 1/Fs
- Ioutmax = maximum current
- RDSmax = maximum high-side MOSFET ON-resistance (see Electrical Characteristics)
- RI = DCR of the inductor
- tdead = dead time (60 ns)