基于PM8805封装系统级芯片的智能以太网供电解决方案

电子工程师 2019-05-11 4367

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描述

ST公司的PM8805是封装系统级芯片，用于以太网供电（PoE）供电器件（PD），可用功率水平高达99.9W.器件嵌入两个有源桥及其驱动电路与驱动高边MOSFET，热插拔MOSFET和兼容IEEE 802.3bt的电池泵.PM8805能进行物理层分类，提供有成效的PSE认证身份证明标识，可确认出4对PSE，信息由专用的Tx信号矩阵来提供。器件由以太网电缆的电源或由外接电源如墙上适配器。 PM8805集成了100V N沟MOSFET，总通路电阻为0.2Ω，100V 0.1Ω高边热插拔MOSFET，PoE-PD单识别标志接口和IEEE 802.3bt/at/af兼容，支持对PoE应用，支持12V辅助源，智能工作模式，热关断保护，主要用在大功率无线数据系统，安全照相机，接入点，公共信息显示以PoE照明系统。本文介绍了PM8805主要特性，内部框图，应用电路，以及大功率PoE PD/5 V高达20A有源箝位正向评估板STEVAL-POE003V1主要特性别，电路图和材料清单以及PCB设计图与装配图。

The PM8805 is a system-in-package for smartpower supply of Power over Ethernet （PoE）Powered Devices （PD） and it is applicable forpower level up to 99.9 W.

It embeds： two active bridges and their drivingcircuitry， a charge pump to drive the high-sideMOSFETs， the hot swap MOSFET and theinterface compliant with IEEE 802.3bt.

The device performs the physical layerclassification， providing the indication ofsuccessful PSE type identification. A 4-pair PSEis identified and the information is available by adedicated matrix of Tx signals.

The device works with power either from theEthernet cable or from an external power sourcesuch as a wall adapter， with possible prevalenceof the auxiliary source with respect to the PoE.

The PM8805 is suitable to build the interfacesection of PoE switch mode power supplies targeting the highest conversion efficiency. Itprovides a PGD signal that can be used to enablea PWM controller， a DC-DC converter or an LEDdriver.

The PM8805 integrates a dual MOSFET bridge and a PD-PoE single-signature interface，specifically designed to support high power， 4-pair （4P） applications， as being specified in the new IEEE802.3bt standard， but also capable of working with high efficiency， 2P applications.

Typically， after the data transformer a diode bridge is used to set a defined polarity to the input voltage since such polarity on the Ethernet cable may vary.

Considering the maximum power levels defined by the IEEE802.3-2015 standard （25 W fora Type2 PD） the diode bridges power losses may still be acceptable， but with new powerhungry applications like UPOE， with more than 50 W at PD end， the power losses of astandard diode bridge become too high.

The same consideration is valid for standard applications that need to squeeze the maximum available power from the PSE. For example， comparing a diode bridge with Vd= 0.8 V with bridged 100 mΩ Ron MOSFETs， the gain at 0.5 A， 50 V is about 0.75 W out of 25W， i.e. about 3% on overall efficiency.

PM8805主要特性：

 Dual active bridge， hot swap MOSFETandPoE-PD interface in a system-in-package

 100 V N-ch MOSFETs with 0.2 Ω total pathresistance for each active bridge.

 100 V， 0.1 Ω high-side N-ch hot swap MOSFET

 PoE-PD single-signature interface compliantwith IEEE 802.3bt / at / af

 Supports 4-pair PoE applications

 Supports 12 V auxiliary sources

 Identifies which kind of PSE （standard orlegacy） is connected with and provides successful IEEE802.3bt/at/af classificationindication as a combination of the T0， T1 andT2 signals （open drain）

 Smart operational modes

 Programmable classification current with3.3 ms delay.

 Optional Autoclass feature

 Advanced energy-saving MPS timings

 Two-step hot swap current protection： DC with1 ms delay and short-circuit with 10 us delay.

 Controlled pre-charge of the output capacitor

 PGD signal （open drain） to enable an externalPWM controller.

 Thermal shutdown protection

PM8805应用：

 High power wireless data systems

 Security cameras

 Access points

 Public information displays

 PoE lighting systems

图1.PM8805内部框图

图2.采用PM8805输入级的PD简化应用电路图

图3.采用PM8805和DC/DC前CM滤波器的PD简化通用电路图

以太网

图4.简化的前辅助连接器电路图

图5.简化的后辅助连接器电路图

图6.PM8805应用案例布局图

大功率PoE PD/5 V高达20A有源箝位正向评估板STEVAL-POE003V1

This evaluation board implements a PoE Class 8 converter that is compliant with the IEEE802.3bt standard. The PoE interface is based on the PM8805 PoE-PD interface and a DC-DC forward active clamp converter based on the PM8804 controller.

The PM8805 system on package device embeds two active bridges and anIEEE802.3bt compliant Powered Device （PD） interface. It can be used in all mediumto-high power 2P and 4P high efficiency PoE and PoE+ applications.

The PM8804 PWM controller integrates all the circuitry required for a smart andefficient 48 V converter， including a programmable oscillator for the switchingfrequency， adjustable slope compensation， dual complementary low-side drivers withprogrammable dead time， programmable soft start， soft turn off and a programmablecurrent sense blanking time.The device targets high efficiency conversion over a wide load range.

The STEVAL-POE003V1consists of a POE interface compliant with the last standard IEEE802.3bt， created withthe PM8805 interface and a forward active clamp DC-DC converter that receives a DC voltage from POEinterface.

PM8805 device integrates two N-channel MOSFET bridges， one for every 2-pair of the POE interface， and anhotswap MOSFET placed in series with the outputs of two bridges. The following figure shows the efficiency of the single forward converter， and the overall efficiency that alsoincludes the power losses of the POE interface.

评估板STEVAL-POE003V1主要特性：

• Features of PM8805

– System in package integrating a double active bridge， a hot-swap MOSFETand a PoE-PD interface

– PoE-PD single-signature interface compliant with IEEE 802.3bt

– Detection and support of high power 4-pair applications

– 100 V N-Ch MOSFETs with 0.2 Ω total path resistance for each activebridge

– Identifies which kind of PSE （standard or legacy） it is connected to andprovides successful IEEE802.3 af / at / bt classification indication as acombination of the T0， T1 and T2 signals （open drain）

– VFQFPN43 8x8 mm with 6 exposed pads

• Features of PM8804

– PWM peak current mode controller

– Input operating voltage up to 75 V

– Internal high voltage start up regulator with 20 mA capability

– Programmable fixed frequency up to 1 Mhz

– Soft start up with settable time

– Soft turn off （optionally disabled）

– Dual 1Apk， low side complementary gate drivers

– GATE2 optionally turned off for reduced consumption

– 80% maximum duty cycle with internal slope compensation

– VFQFPN 3.0x3.0x1.0 16L 0.5 mm pitch