ZHCSK44G December 2009 – November 2022 UCC28C40-Q1 , UCC28C41-Q1 , UCC28C42-Q1 , UCC28C43-Q1 , UCC28C44-Q1 , UCC28C45-Q1
PRODUCTION DATA
- 1 特性
- 2 應(yīng)用
- 3 說明
- 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
- 8.4 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 Input Bulk Capacitor and Minimum Bulk Voltage
- 9.2.2.3 Transformer Turns Ratio and Maximum Duty CycleG
- 9.2.2.4 Transformer Inductance and Peak Currents
- 9.2.2.5 Output Capacitor
- 9.2.2.6 Current Sensing Network
- 9.2.2.7 Gate Drive Resistor
- 9.2.2.8 VREF Capacitor
- 9.2.2.9 RT/CT
- 9.2.2.10 Start-Up Circuit
- 9.2.2.11 Voltage Feedback Compensation
- 9.2.3 Application Curves
- 9.2.4 Power Supply Recommendations
- 9.2.5 Layout
- 10Device and Documentation Support
- 11Mechanical, Packaging, and Orderable Information
封裝選項
機(jī)械數(shù)據(jù) (封裝 | 引腳)
- D|8
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
訂購信息
9.2.2.6 Current Sensing Network
The current sensing network consists of the primary-side current sensing resistor (RCS), filtering components RCSF and CCSF, and optional RP. Typically, the direct current sense signal contains a large amplitude leading edge spike associated with the turnon of the main power MOSFET, reverse recovery of the output rectifier, and other factors including charging and discharging of parasitic capacitances. Therefore, CCSF and RCSF form a low-pass filter that provides immunity to suppress the leading edge spike. For this converter, CCSF is chosen to be 100 pF.
Without RP, RCS sets the maximum peak current in the transformer primary based on the maximum amplitude of the CS pin, which is specified to be 1 V. To achieve 1.36-A primary side peak current, a 0.75-Ω resistor is chosen for RCS.
The high current sense threshold of CS helps to provide better noise immunity to the system but also results in higher losses in the current sense resistor. These current sense losses can be minimized by injecting an offset voltage into the current sense signal using RP. RP and RCSF form a resistor divider network from the current sense signal to the device’s reference voltage (VVREF) which adds an offset to the current sense voltage. This technique still achieves current mode control with cycle-by-cycle over-current protection. To calculate required offset value (VOFFSET), use Equation 16.
Once RP is added, adjust the RCS accordingly.