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[原创] Maxim MAX5995B IEEE 802.3bt兼容PD接口控制器解决方案

关键词:PoE IEEER 802.3af/at/bt 无线通信 建筑物自动化 VOIP

时间:2019-02-04 15:24:28       作者:Maxim       来源:中电网

Maxim公司的MAX5995A/MAX5995B/MAX5995C是IEEE 802.3bt兼容的集成了91W大功率MOSFET的供电设备接口控制器,主要用在以太网供电系统(PoE).器件提供了PD和检测标识,分类标识和集成的具有起动浪涌电流控制的隔离功率开关,简化的墙适配器接口,多事件分类0-8,100V输入最大指标,睡眠模式和超低功耗睡眠模式,主要用在IEEE 802.3bt供电设备,VOIP电话,IP安全班照相机,无线接入点,小型基站和微型基站,照明和建筑物自动化.本文介绍了MAX5995B主要优势和特性,框图, 典型应用电路图以及评估板MAX5995 EVK主要特性,电路图材料清单和PCB设计图.

The MAX5995A/MAX5995B/MAX5995C provide a complete interface for a powered device (PD) to comply with the IEEER 802.3af/at/bt standard in a Power-Over-Ethernet(PoE) system. The devices provide the PD with a detection signature, classification signature, and an integrated isolation power switch with startup inrush current control.

During the startup period, the devices limit the current to 135mA (typ) before switching to the higher current limit (1800mA to 2400mA, typ) when the isolation power MOSFET is fully enhanced. The devices feature Multi-Event classification, Intelligent MPS (MAX5995B/MAX5995C), Autoclass (MAX5995C), an input UVLO with wide hysteresis and long deglitch time to compensate for twistedpair cable resistive drop and to assure glitch-free transition during power-on/-off conditions. The devices can withstand a maximum voltage of 100V at the input.

The devices support a Multi-Event classification method, as specified in the IEEE 802.3bt standard, and provide a signal to indicate from Type 1 to Type 4 Power Sourcing Equipment (PSE). The devices can detect the presence of a wall adapter power source connection and allow a smooth switch-over from the PoE power source to the wall power adapter.

The devices also provide a power-good (PG) signal, twostep current limit and foldback control, overtemperature protection. A sleep mode feature in the MAX5995A/MAX5995B minimizes low power consumption while generating the Maintain Power Signature (MPS) to maintain PSE connection. An Ultra-Low-Power sleep mode feature in the MAX5995A/MAX5995B further reduces power consumption while still generating MPS current. The MAX5995B/MAX5995C provides Intelligent Maintain Power Signature (IMPS) feature to automatically enable MPS current by detecting the port current.The devices feature a LED driver that is activated during sleep mode, Ultra-Low-Power sleep mode(MAX5995A/MAX5995B), and Intelligent MPS mode(MAX5995B/MAX5995C). Multi-Event indication feature provides patterned signals to indicate power level allocated from PSE to PD in 5 different scenarios.

The MAX5995C provides Autoclass feature to enable advanced applications that allow the PSE to effectively optimize power allocation to PD.

The MAX5995A/MAX5995B/MAX5995C are available in a 16-pin, 5mm x 5mm, TQFN power package. These devices are rated over the -40oC to +85oC temperature range.

MAX5995B主要优势和特性:

● IEEE 802.3af/at/bt Compliant
● Type 1~4 PSE Classification Indicator or an External Wall Adapter Indicator Output
● Simplified Wall Adapter Interface
● Multi-Event Classification 0–8
● Intelligent MPS (MAX5995B/MAX5995C, Patent US9152161)
● Sleep Mode and Ultra-Low-Power Sleep Mode (MAX5995A/MAX5995B)
● 100V Input Absolute Maximum Rating
● Inrush Current Limit During Startup
● Current Limit During Normal Operation
● Current Foldback Protection
● Undervoltage Lockout at 36V
● LED Driver with Programmable LED Current (MAX5995A/MAX5995B)
● Overtemperature Protection
● Multi-Event Power Level Indication
● Autoclass Feature (MAX5995C)
● Thermally Enhanced, 5mm x 5mm, 16-Pin TQFN

MAX5995B应用:

● IEEE 802.3bt Powered Devices
● VOIP Phones, IP Security Cameras
● Wireless Access Point
● Small Cell, Pico Cell
● Lighting
● Building Automation

图1. MAX5995B简化框图

图2. MAX5995A/B功能框图

图3.MAX5995C框图

图4. MAX5995A/B典型应用电路图

图5. MAX5995C典型应用电路图

评估板MAX5995 EVK

The MAX5995 evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board featuring an Ethernet port, network powered-device (PD) interface controller circuit for -57V supply rail systems. The EV kit uses the MAX5995B IEEE® 802.3af/at/bt-compliant network PD interface controller in a 16-pin TQFN package with an exposed pad. The IC is used in Power-over- Ethernet (PoE) applications requiring DC power from an Ethernet network port for PDs such as VoIP phones, wireless access nodes, security cameras, lighting, and building automation.

The EV kit receives power from IEEE 802.3af/at/bt-compliant power-sourcing equipment (PSE). Refer to the MAX5952, MAX5965A/MAX5965B, and MAX5980 IC data sheets for PSE controllers. The PSE provides the required -36V to -57V DC power over an unshielded twisted-pair Ethernet network cable to the EV kit’s RJ45 magnetic jack. The EV kit features a 1 x 1 Gigabit RJ45 magnetic jack and two active full-wave rectifiers (N101 and N102) for separating the DC power provided by an endspan or midspan Ethernet system.

The EV kit can also be powered by a wall adapter power source. The EV kit provides PCB pads to accept the output of a wall adapter power source. When a wall adapter power source is detected, it always takes precedence over the PSE source and allows the wall adapter to power the EV kit.

The EV kit demonstrates the full functionality of the IC, such as PD detection signature, PD classification signature, Multi-Event Classification (MEC), Intelligent MPS, inrush current control, input undervoltage lockout (UVLO), and DC-DC step-down converter. The step-down converter operates at a fixed 290kHz switching frequency and is configured for an isolated active-clamped forward topology with output voltage +12V DC that can deliver 5.5A of current.

评估板MAX5995 EVK主要特性:

IEEE 802.3af/at/bt-Compliant PD Interface Circuit
Multi-Event Classification 0-8
-36V to -57V Input Range
Demonstrates a 71W PD Design with Isolated Active- Clamped Forward Topology DC-DC Converter
+12V Output at 5.5A
Startup Inrush Current Limit of 135mA (typ)
Current Limit During Normal Operation
Evaluates Endspan and Midspan Ethernet Systems
Type 1-4 PSE Classification Indicator
Simplified Wall Adapter Interface
Demonstrates Sleep and Ultra-Sleep Power-Saving Modes
Proven PCB Layout
Fully Assembled and Tested

图6. 评估板MAX5995 EVK电路图(1)

图7. 评估板MAX5995 EVK电路图(2)

图8. 评估板MAX5995 EVK电路图(3)
评估板MAX5995 EVK材料清单:




图9. 评估板MAX5995 EVK PCB设计图(1):顶层丝印

图10. 评估板MAX5995 EVK PCB设计图(2):顶层图

图11. 评估板MAX5995 EVK PCB设计图(3):GND

图12. 评估板MAX5995 EVK PCB设计图(4):PWR


图13. 评估板MAX5995 EVK PCB设计图(5):底层图

图14. 评估板MAX5995 EVK PCB设计图(6):底层丝印
详情请见:
https://datasheets.maximintegrated.com/en/ds/MAX5995A-MAX5995C.pdf
https://datasheets.maximintegrated.com/en/ds/MAX5995BEVKIT.pdf
MAX5995A-MAX5995C.pdf
MAX5995BEVKIT.pdf

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