ZHCSIB2B December 2017 – October 2019 UCC28064A
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 说明 （续）
- 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 Principles of Operation
- 8.3.2 Natural Interleaving
- 8.3.3 On-Time Control, Maximum Frequency Limiting, Restart Timer and Input Voltage Feed-Forward compensation
- 8.3.4 Distortion Reduction
- 8.3.5 Zero-Current Detection and Valley Switching
- 8.3.6 Phase Management and Light-Load Operation
- 8.3.7 Burst Mode Operation
- 8.3.8 External Disable
- 8.3.9 Improved Error Amplifier
- 8.3.10 Soft Start
- 8.3.11 Brownout Protection
- 8.3.12 Line Dropout Detection
- 8.3.13 VREF
- 8.3.14 VCC
- 8.3.15
System Level Protections
- 8.3.15.1 Failsafe OVP - Output Over-voltage Protection
- 8.3.15.2 Overcurrent Protection
- 8.3.15.3 Open-Loop Protection
- 8.3.15.4 VCC Undervoltage Lock-Out (UVLO) Protection
- 8.3.15.5 Phase-Fail Protection
- 8.3.15.6 CS - Open, TSET - Open and Short Protection
- 8.3.15.7 Thermal Shutdown Protection
- 8.3.15.8 Fault Logic Diagram
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Custom Design With WEBENCH® Tools
- 9.2.2.2 Inductor Selection
- 9.2.2.3 ZCD Resistor Selection RZA, RZB
- 9.2.2.4 HVSEN
- 9.2.2.5 Output Capacitor Selection
- 9.2.2.6 Selecting RS For Peak Current Limiting
- 9.2.2.7 Power Semiconductor Selection (Q1, Q2, D1, D2)
- 9.2.2.8 Brownout Protection
- 9.2.2.9 Converter Timing
- 9.2.2.10 Programming VOUT
- 9.2.2.11 Voltage Loop Compensation
- 9.2.3 Application Curves
- 10Power Supply Recommendations
- 11Layout
- 12Package Option Addendum
- 13器件和文档支持
- 14机械、封装和可订购信息
9.2.2.6 Selecting RS For Peak Current Limiting
The UCC28064A peak limit comparator senses the total input current and is used to protect the MOSFETs during inrush and over-load conditions. For reliability, the peak current limit (IPEAK) threshold in this design is set for 120% of the nominal maximum current that will be observed during power up, as shown in Equation 34.
A standard 15-mΩ metal-film current-sense resistor will be used for current sensing, as shown in Equation 35. The estimated power loss of the current-sense resistor (PRS) is less than 0.25 W during normal operation, as shown in Figure 8.
The most critical parameter in selecting a current-sense resistor is the surge rating. The resistor needs to withstand a short-circuit current larger than the current required to open the fuse (F1). I2t (ampere-squared- seconds) is a measure of thermal energy resulting from current flow required to melt the fuse, where I2t is equal to RMS current squared times the duration of the current flow in seconds. A 4-A fuse with an I2t of 14 A2s was chosen to protect the design from a short-circuit condition. To ensure the current-sense resistor has high-enough surge protection, a 15-mΩ, 500-mW, metal-strip resistor was chosen for the design. The resistor has a 2.5-W surge rating for 5 seconds. This result translates into 833 A2s and has a high-enough I2t rating to survive a short-circuit before the fuse opens, as described in Equation 37.
