ZHCSHL4I October 2008 – December 2017 TPS23754 , TPS23754-1 , TPS23756
PRODUCTION DATA.
- 1 特性
- 2 應用
- 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
- 7.4.1
PoE Overview
- 7.4.1.1 Threshold Voltages
- 7.4.1.2 PoE Start-Up Sequence
- 7.4.1.3 Detection
- 7.4.1.4 Hardware Classification
- 7.4.1.5 Inrush and Start-Up
- 7.4.1.6 Maintain Power Signature
- 7.4.1.7 Start-Up and Converter Operation
- 7.4.1.8 PD Hotswap Operation
- 7.4.1.9 Converter Controller Features
- 7.4.1.10 Bootstrap Topology
- 7.4.1.11 Current Slope Compensation and Current Limit
- 7.4.1.12 Blanking – RBLNK
- 7.4.1.13 Dead Time
- 7.4.1.14 FRS and Synchronization
- 7.4.1.15 T2P, Start-Up, and Power Management
- 7.4.1.16 Thermal Shutdown
- 7.4.1.17 Adapter ORing
- 7.4.1.18 PPD ORing Features
- 7.4.1.19 Using DEN to Disable PoE
- 7.4.1.20 ORing Challenges
- 7.4.1
PoE Overview
-
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 Dead Time Resistor, RDT
- 8.2.2.7 Switching Transformer Considerations and RVC
- 8.2.2.8 Special Switching MOSFET Considerations
- 8.2.2.9 Thermal Considerations and OTSD
- 8.2.2.10 APD Pin Divider Network, RAPD1, RAPD2
- 8.2.2.11 PPD Pin Divider Network, RPPD1, RPPD2
- 8.2.2.12 Setting Frequency (RFRS) and Synchronization
- 8.2.2.13 Current Slope Compensation
- 8.2.2.14 Blanking Period, RBLNK
- 8.2.2.15 Estimating Bias Supply Requirements and CVC
- 8.2.2.16 T2P Pin Interface
- 8.2.2.17 Advanced ORing Techniques
- 8.2.2.18 Soft Start
- 8.2.2.19 Frequency Dithering for Conducted Emissions Control
- 8.2.3 Application Curves
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機械、封裝和可訂購信息
封裝選項
請參考 PDF 數據表獲取器件具體的封裝圖。
機械數據 (封裝 | 引腳)
- PWP|20
散熱焊盤機械數據 (封裝 | 引腳)
- PWP|20
訂購信息
8.2.2.15 Estimating Bias Supply Requirements and CVC
The bias supply (VC) power requirements determine the CVC sizing and frequency of hiccup during a fault. The first step is to determine the power and current requirements of the power supply control, then use this to select CVC. The control current draw will be assumed constant with voltage to simplify the estimate, resulting in an approximate value.
First determine the switching MOSFET gate drive power.
- Let VQG be the gate voltage swing that the MOSFET QG is rated to (often 10 V).
- Compute gate drive power if VC is 12 V, QGATE is 17 nC, and QGAT2 is 8 nC.
PDRIVE = 61.2 mW + 28.8 mW = 90 mW- This illustrates why MOSFET QG should be an important consideration in selecting the switching MOSFETs.
- Estimate the required bias current at some intermediate voltage during the CVC discharge. For the TPS23754 device, 12 V provides a reasonable estimate. Add the operating bias current to the gate drive current.
- ITOTAL = IDRIVE + IOPERATING = 7.5 mA + 0.92 mA = 8.42 mA
- Compute the required CVC based on start-up within the typical soft-start period of 4 ms.
- For this case, a standard 10-μF electrolytic plus a 0.47 μF should be sufficient.
- Compute the initial time to start the converter when operating from PoE.
- Using a typical bootstrap current of 4 mA, compute the time to start-up.
- Compute the fault duty cycle and hiccup frequency:
- The optocoupler current is 0 mA because the output is in current limit.
- Also, it is assumed IT2P is 0 mA.
- With the TPS23754 device, the voltage rating of CVC1 and CVC2 should be 25 V minimum while with the TPS23756 rating can be 16 V.