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TPS23757
SLVS948D – JULY 2009 – REVISED NOVEMBER 2013
www.ti.com
Use of diode D VDD for PoE priority may dictate the use of additional protection around the TPS23757. ESD
events between the PD power inputs (PoE and adapter), or the inputs and converter output, cause large stresses
in the hotswap MOSFET if D VDD becomes reverse biased and transient current around the TPS23757 is blocked.
The use of C VDD and D RTN in Figure 24 provides additional protection should over-stress of the TPS23757 be an
issue. An SMAJ58A would be a good initial selection for D RTN . Individual designs may have to tune the value of
C VDD .
C VDD
0.01 m F
D VDD
PPD
DEN
CLS
V SS
Figure 24. Example of Added ESD Protection for PoE Priority
Capacitor, C 1
The standard specifies an input bypass capacitor (from V DD to V SS ) of 0.05 μ F to 0.12 μ F. Typically a 0.1 μ F, 100
V, 10% ceramic capacitor is used.
Detection Resistor, R DEN
The standard specifies a detection signature resistance, R DEN between 23.7 k ? and 26.3 k ? , or 25 k ? ± 5%.
Choose an R DEN of 24.9 k ? .
Classification Resistor, R CLS
Connect a resistor from CLS to V SS to program the classification current according to the IEEE 802.3at standard.
The class power assigned should correspond to the maximum average power drawn by the PD during operation.
Select R CLS according to Table 1 . The TPS23757 should not use class 4 as its input current is limited to class 3
(and lower) levels. Apart from power above 13W, there is no advantage to type 2 operation.
APD Pin Divider Network, R APD1 , R APD2
The APD pin can be used to disable the TPS23757 internal hotswap MOSFET giving the adapter source priority
over the PoE source. An example calculation is provided in (TI literature number) SLVA306A .
PPD Pin Divider Network, R PPD1 , R PPD2
The PPD pin can be used to override the internal hotswap MOSFET UVLO (UVLO_R and UVLO_H) when using
low voltage adapters connected between V DD and V SS . The PPD pin has an internal 5 μ A pulldown current
source. As an example, consider the choice of R PPD1 and R PPD2 , for a 24 V adapter.
1. Select the startup voltage, V ADPTR-ON approximately 75% of nominal for a 24 V adapter. Assuming that the
adapter output is 24 V ± 10%, this provides 15% margin below the minimum adapter operating voltage.
2. Choose V ADPTR-ON = 24 V × 0.75 = 18 V
3. Choose R PPD2 = 3.01 k ?
4. Calculate R PPD1
24
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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