ZHCSA47E July 2012 – January 2018 TPS23751 , TPS23752
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
-
6 Specifications
- 6.1 Absolute Maximum Ratings
- 6.2 ESD Ratings
- 6.3 ESD Ratings: Surge
- 6.4 Recommended Operating Conditions
- 6.5 Thermal Information
- 6.6 Electric Characteristics - Controller Section
- 6.7 Electrical Characteristics - Sleep Mode (TPS23752 Only)
- 6.8 Electrical Characteristics - PoE Interface Section
- 6.9 Typical Characteristics
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagrams
- 7.3 Feature Description
- 7.4
Device Functional Modes
- 7.4.1 PoE Overview
- 7.4.2
Sleep Mode Operation (TPS23752 only)
- 7.4.2.1 Converter Controller Features
- 7.4.2.2 PWM and VFO Operation; CTL, SRT, and SRD Pin Relationships to Output Load Current
- 7.4.2.3 Bootstrap Topology
- 7.4.2.4 Current Slope Compensation and Current Limit
- 7.4.2.5 RT
- 7.4.2.6 T2P, Startup and Power Management
- 7.4.2.7 Thermal Shutdown
- 7.4.2.8 Adapter ORing
- 7.4.2.9 Using DEN to Disable PoE
- 7.4.2.10 ORing Challenges
-
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 Input Bridges and Schottky Diodes
- 8.2.2.2 Protection, D1
- 8.2.2.3 Capacitor, C1
- 8.2.2.4 Detection Resistor, RDEN
- 8.2.2.5 Classification Resistor, RCLS
- 8.2.2.6 APD Pin Divider Network, RAPD1, RAPD2
- 8.2.2.7 Setting the PWM-VFO Threshold using the SRT pin
- 8.2.2.8 Setting Frequency (RT)
- 8.2.2.9 Current Slope Compensation
- 8.2.2.10 Voltage Feed-Forward Compensation
- 8.2.2.11 Estimating Bias Supply Requirements and Cvc
- 8.2.2.12 Switching Transformer Considerations and RVC
- 8.2.2.13 T2P Pin Interface
- 8.2.2.14 Softstart
- 8.2.2.15 Special Switching MOSFET Considerations
- 8.2.2.16 ESD
- 8.2.2.17 Thermal Considerations and OTSD
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
8.2.2.11 Estimating Bias Supply Requirements and Cvc
The bias supply (VC) power requirements determine CVC sizing and hiccup frequency during a fault. The first step is to determine the power and current requirements of the power supply control circuitry, then select CVC. The following example assumes that control current draw is constant with voltage with no loading by the feedback and T2P optocouplers to simplify the process:
- Let VQG be the gate voltage swing that the MOSFET QG is rated to (often 10 V).
- Estimate the required bias current at some intermediate voltage during the CVC discharge. For the TPS23751 and TPS23752, 12 V provides a reasonable estimate. Add the operating bias current to the gate drive current.
- Compute the required CVC based on startup within the typical softstart delay of 3.01 ms.
- Choose a 10 μF electrolytic and 0.47 μF ceramic capacitor each rated for 16 V (minimum). Compute the initial time to start the converter when operating from PoE. Using a typical bootstrap current of 1.5 mA, compute the time to startup.
- Compute the fault duty cycle and hiccup frequency
Equation 6. 
Compute gate drive power if VC is 12 V and QGATE is 17 nC
Equation 7. 
This equation illustrates why MOSFET QG should be an important consideration in selecting the switching MOSFETs.
Equation 8. 
Equation 9. 
Equation 10. 
Equation 11. 
Equation 12. 
Equation 13. 
Equation 14. 