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TPS23757
www.ti.com
SLVS948D – JULY 2009 – REVISED NOVEMBER 2013
DETAILED DESCRIPTION
PoE OVERVIEW
The following text is intended as an aid in understanding the operation of the TPS23757 but not as a substitute
for the IEEE 802.3at standard. The IEEE 802.3at standard is an update to IEEE 802.3-2008 clause 33 (PoE),
adding high-power options and enhanced classification. Generally speaking, a device compliant to IEEE 802.3-
2008 will be referred to as a type 1 device (PD or PSE), and devices with high power and enhanced
classification will be referred to as type 2 devices (PD or PSE). Standards change and should always be
referenced when making design decisions. The TPS23757 supports type 1 PDs as a result of the limited-current
capability and lack of type 2 hardware class detection. Type 1 devices are encompassed within the new
standard, providing the same features and functions as devices in service since 2003.
The IEEE 802.3at standard defines a method of safely powering a PD over a cable by power sourcing equipment
(PSE), and then removing power if a PD is disconnected. The process proceeds through an idle state and three
states of detection, classification, and operation. The PSE leaves the cable unpowered (idle state) while it
periodically looks to see if something has been plugged in; this is referred to as detection. The low power levels
used during detection are unlikely to damage devices not designed for PoE. If a valid PD signature is present,
the PSE my inquire how much power the PD requires; this is referred to as classification. The PSE may then
power the PD if it has adequate capacity.
Type 2 PSEs are required to do type 1 hardware classification plus a (new) data-layer classification, or an
enhanced type 2 hardware classification. Type 1 PSEs are not required to do hardware or data link layer (DLL)
classification. A type 2 PD must do type 2 hardware classification as well as DLL classification. A type 1 PD may
have passive classification ( class 0, < 5 mA) or active type 1 hardware class (1 through 3) per IEEE 802.3-2008.
DLL communication occurs after power-on and the ethernet data link has been established by the applications
circuits in the PD (not the power interface). It may be used by type 1 PDs and must be implemented by type 2
PDs.
Once started, the PD must present the maintain power signature (MPS) to assure the PSE that it is still present.
The PSE monitors its output for a valid MPS, and turns the port off if it loses the MPS. Loss of the MPS returns
the PSE to the idle state. Figure 18 shows the operational states as a function of PD input voltage. The upper
half is for IEEE 802.3-2008, and the lower half shows specific differences for IEEE 802.3at. The dashed lines in
the lower half indicate these are the same (e.g., detect and class) for both.
Detect
6.9
Classify
Shut-
down
Normal Operation
42.5
0
2.7
10.1 14.5
20.5
30
37
42
57 PI Voltage (V)
Mark
Normal Operation
Figure 18. Operational States for PD
Copyright ? 2009–2013, Texas Instruments Incorporated
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相关代理商/技术参数
TPS23757PW 功能描述:热插拔功率分布 Hi Eff PoE Inter & DC/DC Controller RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS23757PWR 功能描述:热插拔功率分布 Hi Eff PoE Interface & DC/DC Controller RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS2375D 功能描述:热插拔功率分布 IEEE 802.3af PoE Pwr Device Cntrler RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS2375D 制造商:Texas Instruments 功能描述:POWER OVER ETHERNET ((NW))
TPS2375DG4 功能描述:热插拔功率分布 IEEE 802.3af PoE Pwr Device Cntrler RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS2375DR 功能描述:热插拔功率分布 IEEE 802.3af PoE Pwr Device Cntrler RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS2375DRG4 功能描述:热插拔功率分布 IEEE 802.3af PoE Pwr Device Cntrler RoHS:否 制造商:Texas Instruments 产品:Controllers & Switches 电流限制: 电源电压-最大:7 V 电源电压-最小:- 0.3 V 工作温度范围: 功率耗散: 安装风格:SMD/SMT 封装 / 箱体:MSOP-8 封装:Tube
TPS2375EVM 功能描述:电源管理IC开发工具 TPS2375 POE Powed Device Eval Mod RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V