ZHCSHY7A April 2018 – May 2018 UCC28742
PRODUCTION DATA.
- 1 特性
- 2 應(yīng)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
- 7.4 Device Functional Modes
-
8 Applications 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 VDD Capacitance, CDD
- 8.2.2.3 VDD Start-Up Resistance, RSTR
- 8.2.2.4 Input Bulk Capacitance and Minimum Bulk Voltage
- 8.2.2.5 Transformer Turns Ratio, Inductance, Primary-Peak Current
- 8.2.2.6 Transformer Parameter Verification
- 8.2.2.7 VS Resistor Divider and Line Compensation
- 8.2.2.8 Standby Power Estimate
- 8.2.2.9 Output Capacitance
- 8.2.2.10 Feedback Loop Design Consideration
- 8.2.3 Application Curves
- 8.3 Do's and Don'ts
- 9 Power Supply Recommendations
- 10Layout
-
11器件和文檔支持
- 11.1
器件支持
- 11.1.1 開發(fā)支持
- 11.1.2
器件命名規(guī)則
- 11.1.2.1 電容術(shù)語（以法拉為單位）
- 11.1.2.2 占空比術(shù)語
- 11.1.2.3 頻率術(shù)語（以赫茲為單位）
- 11.1.2.4 電流術(shù)語（以安培為單位）
- 11.1.2.5 電流和電壓調(diào)節(jié)術(shù)語
- 11.1.2.6 變壓器術(shù)語
- 11.1.2.7 功率術(shù)語（以瓦特為單位）
- 11.1.2.8 電阻術(shù)語（以 Ω 為單位）
- 11.1.2.9 時(shí)序術(shù)語（以秒為單位）
- 11.1.2.10 電壓術(shù)語（以伏特為單位）
- 11.1.2.11 交流電壓術(shù)語（以 VRMS 為單位）
- 11.1.2.12 效率術(shù)語
- 11.2 文檔支持
- 11.3 接收文檔更新通知
- 11.4 社區(qū)資源
- 11.5 商標(biāo)
- 11.6 靜電放電警告
- 11.7 術(shù)語表
- 11.1
器件支持
- 12機(jī)械、封裝和可訂購信息
封裝選項(xiàng)
機(jī)械數(shù)據(jù) (封裝 | 引腳)
- DBV|6
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
訂購信息
7.3.5 Valley-Switching and Valley-Skipping
The UCC28742 utilizes valley switching to reduce switching losses in the MOSFET, reduce induced-EMI, and minimize the turn-on current spike at the sense resistor. The controller operates in valley-switching in all load conditions unless the VDS ringing diminished.
Referring to Figure 16 below, the UCC28742 operates in a valley-skipping mode in most load conditions to maintain an accurate voltage or current regulation point and still switch on the lowest available VDS voltage.
Figure 16. Valley-Skipping Mode The UCC28742 forces a controlled minimum switching period corresponding to the power supply operating frequency. In each switching cycle, after the minimum period is expired, the UCC28742 looks for the next resonant valley on the auxiliary winding. The controller initiates a new power cycle at this valley point which corresponds to a reduced voltage level on the power MOSFET. If at the point in time when the minimum period expires ringing on the transformer winding has decayed such that no further resonant valleys can be detected a new power cycle is initiated following a fixed time, tZTO. This also applies when primary inductance LP is designed with a high value that causes de-mag end ringing cycle longer than tZTO. When either happens, the valley switching is lost but the converter output voltage will still be in regulation.