ZHCSJ42 December 2018 TPS54340B
PRODUCTION DATA.
- 1 特性
- 2 應用
- 3 說明
- 4 修訂歷史記錄
- 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 Output Current
- 7.3.3 Pulse Skip Eco-mode
- 7.3.4 Low Dropout Operation and Bootstrap Voltage (BOOT)
- 7.3.5 Error Amplifier
- 7.3.6 Adjusting the Output Voltage
- 7.3.7 Enable and Adjusting Undervoltage Lockout
- 7.3.8 Internal Soft Start
- 7.3.9 Constant Switching Frequency and Timing Resistor (RT/CLK) pin)
- 7.3.10 Accurate Current Limit Operation and Maximum Switching Frequency
- 7.3.11 Synchronization to RT/CLK pin
- 7.3.12 Overvoltage Protection
- 7.3.13 Thermal Shutdown
- 7.3.14 Small Signal Model for Loop Response
- 7.3.15 Simple Small Signal Model for Peak-Current-Mode Control
- 7.3.16 Small Signal Model for Frequency Compensation
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Application: Buck Converter
- 8.2.1 Design Requirements
- 8.2.2
Detailed Design Procedures
- 8.2.2.1 Custom Design with WEBENCH® Tools
- 8.2.2.2 Selecting the Switching Frequency
- 8.2.2.3 Output Inductor Selection (LO)
- 8.2.2.4 Output Capacitor
- 8.2.2.5 Catch Diode
- 8.2.2.6 Input Capacitor
- 8.2.2.7 Bootstrap Capacitor Selection
- 8.2.2.8 Undervoltage Lockout Setpoint
- 8.2.2.9 Output Voltage and Feedback Resistors Selection
- 8.2.2.10 Minimum VIN
- 8.2.2.11 Compensation
- 8.2.2.12 Discontinuous Conduction Mode and Eco-mode Boundary
- 8.2.2.13 Power Dissipation
- 8.2.3 Application Curves
- 8.3 Other Applications
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機械、封裝和可訂購信息
7.3.7 Enable and Adjusting Undervoltage Lockout
The TPS54340B is enabled when the VIN pin voltage rises above 4.3 V, and the EN pin voltage exceeds the enable threshold of 1.2 V. The TPS54340B is disabled when the VIN pin voltage falls below 4 V or when the EN pin voltage is below 1.2 V. The EN pin has an internal pullup current source, i1, of 1.2 μA that enables operation of the TPS54340B when the EN pin floats.
If an application requires a higher undervoltage lockout (UVLO) threshold, use the circuit shown in Figure 22 to adjust the input voltage UVLO with two external resistors. When the EN pin voltage exceeds 1.2 V, an additional 3.4 μA of hysteresis current, Ihys, is sourced out of the EN pin. When the EN pin is pulled below 1.2 V, the 3.4 μA Ihys current is removed. This addional current facilitates adjustable input voltage UVLO hysteresis. Use Equation 4 to calculate RUVLO1 for the desired UVLO hysteresis voltage. Use Equation 5 to calculate RUVLO2 for the desired VIN start voltage.
In applications designed to start at relatively low input voltages (for example, from 4.5 V to 9 V) and withstand high input voltages (for example, from 40 V to 42 V), the EN pin may experience a voltage greater than the absolute maximum voltage of 8.4 V during the high input voltage condition. It is recommended to use a zener diode to clamp the pin voltage below the absolute maximum rating.
Figure 22. Adjustable Undervoltage Lockout (UVLO) 
