ZHCSL72B October 2016 – July 2021 TPS57114C-Q1
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3 Feature Description
- 7.4
Device Functional Modes
- 7.4.1 Adjusting the Output Voltage
- 7.4.2 Enable Functionality and Adjusting Undervoltage Lockout
- 7.4.3 Slow-Start or Tracking Pin
- 7.4.4 Sequencing
- 7.4.5 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
- 7.4.6 Overcurrent Protection
- 7.4.7 Frequency Shift
- 7.4.8 Reverse Overcurrent Protection
- 7.4.9 Synchronize Using The RT/CLK Pin
- 7.4.10 Power Good (PWRGD Pin)
- 7.4.11 Overvoltage Transient Protection
- 7.4.12 Thermal Shutdown
- 7.4.13 Small-Signal Model for Loop Response
- 7.4.14 Simple Small-Signal Model for Peak-Current Mode Control
- 7.4.15 Small-Signal Model for Frequency Compensation
-
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 Selecting the Switching Frequency
- 8.2.2.2 Output Inductor Selection
- 8.2.2.3 Output Capacitor
- 8.2.2.4 Input Capacitor
- 8.2.2.5 Slow-Start Capacitor
- 8.2.2.6 Bootstrap Capacitor Selection
- 8.2.2.7 Output-Voltage And Feedback-Resistor Selection
- 8.2.2.8 Compensation
- 8.2.2.9 Power-Dissipation Estimate
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
7.4.14 Simple Small-Signal Model for Peak-Current Mode Control
Figure 7-11 is a simple small-signal model that one can use to understand how to design the frequency compensation. An approximation of a voltage-controlled current source (duty-cycle modulator) supplying current to the output capacitor and load resistor can approximate the TPS57114C-Q1 power stage. The control-to-output transfer function, shown in Equation 10, consists of a dc gain, one dominant pole, and one ESR zero. The quotient of the change in switch current divided by the change in COMP pin voltage (node c in Figure 7-11) is the power-stage transconductance. The gm for the TPS57114C-Q1 device is 25 S. The low-frequency gain of the power-stage frequency response is the product of the transconductance and the load resistance, as shown in Equation 11. As the load current increases and decreases, the low-frequency gain decreases and increases, respectively. This variation with load may seem problematic at first glance, but the dominant pole moves with load current (see Equation 12). The dashed line in the right half of Figure 7-12 highlights the combined effect. As the load current decreases, the gain increases and the pole frequency lowers, keeping the 0-dB crossover frequency the same for the varying load conditions, which makes it easier to design the frequency compensation.
Figure 7-12 Simple Small-Signal Model and Frequency Response for Peak-Current-Mode Control
