ZHCS979F June 2012 – October 2020 TPS53318 , TPS53319
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 5-V LDO and VREG Start-Up
- 8.3.2 Adaptive On-Time D-CAP Control and Frequency Selection
- 8.3.3 Ramp Signal
- 8.3.4 Adaptive Zero Crossing
- 8.3.5 Output Discharge Control
- 8.3.6 Power-Good
- 8.3.7 Current Sense, Overcurrent, and Short Circuit Protection
- 8.3.8 Overvoltage and Undervoltage Protection
- 8.3.9 Redundant Overvoltage Protection (OVP)
- 8.3.10 UVLO Protection
- 8.3.11 Thermal Shutdown
- 8.3.12 Small Signal Model
- 8.3.13 External Component Selection Using All Ceramic Output Capacitors
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Applications
- 9.2.1
Application Using Bulk Output Capacitors, Redundant Overvoltage Protection Function (OVP) Disabled
- 9.2.1.1 Design Requirements
- 9.2.1.2
Detailed Design Procedure
- 9.2.1.2.1 Step One: Select Operation Mode and Soft-Start Time
- 9.2.1.2.2 Step Two: Select Switching Frequency
- 9.2.1.2.3 Step Three: Choose the Inductor
- 9.2.1.2.4 Step Four: Choose the Output Capacitor or Capacitors
- 9.2.1.2.5 Step Five: Determine the Value of R1 and R2
- 9.2.1.2.6 Step Six: Choose the Overcurrent Setting Resistor
- 9.2.1.3 Application Curves
- 9.2.2 Application Using Ceramic Output Capacitors, Redundant Overvoltage Protection Function (OVP) Enabled
- 9.2.1
Application Using Bulk Output Capacitors, Redundant Overvoltage Protection Function (OVP) Disabled
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.12 Small Signal Model
From small-signal loop analysis, a buck converter using D-CAP mode can be simplified as shown in Figure 8-4.
Figure 8-4 Simplified Modulator ModelThe output voltage is compared with the internal reference voltage (ramp signal is ignored here for simplicity). The PWM comparator determines the timing to turn on the high-side MOSFET. The gain and speed of the comparator can be assumed high enough to keep the voltage at the beginning of each on cycle substantially constant.
For loop stability, the 0-dB frequency, ƒ0, defined below needs to be lower than 1/4 of the switching frequency.
According to Equation 7, the loop stability of D-CAP mode modulator is mainly determined by the chemistry of the capacitor. For example, specialty polymer capacitors (SP-CAP) have an output capacitance in the order of several 100 µF and ESR in range of 10 mΩ. These make ƒ0 on the order of 100 kHz or less, creating a stable loop. However, ceramic capacitors have an ƒ0 at more than 700 kHz, and need special care when used with this modulator. An application circuit for ceramic capacitor is described in Section 8.3.13.