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TPS23757
www.ti.com
SLVS948D – JULY 2009 – REVISED NOVEMBER 2013
Special Switching MOSFET Considerations
Special care must be used in selecting the converter switching MOSFET. The TPS23757 minimum switching
MOSFET V GATE is ~5.5 V, which is due to the V C lower threshold. This will occur during an output overload, or
towards the end of a (failed) bootstrap startup. The MOSFET must be able to carry the anticipated peak fault
current at this gate voltage.
Thermal Considerations and OTSD
Sources of nearby local PCB heating should be considered during the thermal design. Typical calculations
assume that the TPS23757 is the only heat source contributing to the PCB temperature rise. It is possible for a
normally operating TPS23757 device to experience an OTSD event if it is excessively heated by a nearby
device.
Frequency Dithering for Conducted Emissions Control
The international standard CISPR 22 (and adopted versions) is often used as a requirement for conducted
emissions. Ethernet cables are covered as a telecommunication port under section 5.2 for conducted emissions.
Meeting EMI requirements is often a challenge, with the lower limits of Class B being especially hard. Circuit
board layout, filtering, and snubbing various nodes in the power circuit are the first layer of control techniques. A
more detailed discussion of EMI control is presented in Practical Guidelines to Designing an EMI Compliant PoE
Powered Device With Isolated Flyback, TI literature number SLUA469 . Additionally, IEEE802.3at sections 33.3
and 33.4 have requirements for noise injected onto the Ethernet cable based on compatibility with data
transmission.
Occasionally, a technique referred to as frequency dithering is utilized to provide additional EMI measurement
reduction. The switching frequency is modulated to spread the narrowband individual harmonics across a wider
bandwidth, thus lowering peak measurements. The circuit of Figure 32 modulates the switching frequency by
feeding a small ac signal into the FRS pin. These values may be adapted to suit individual needs.
V B
+
-
6.04k W
TL331IDBV
10k W
To
301k W
1 m F
FRS
ARTN
Figure 32. Frequency Dithering
ESD
The TPS23757 has been tested to EN61000-4-2 using a power supply based on Figure 1 . The levels used were
8 kV contact discharge and 15 kV air discharge. Surges were applied between the PoE input and the dc output,
between the adapter input and the dc output, between the adapter and the PoE inputs, and to the dc output with
respect to earth. Tests were done both powered and unpowered. No TPS23757 failures were observed and
operation was continuous. See Figure 24 for additional protection for some test configurations.
ESD requirements for a unit that incorporates the TPS23757 have a much broader scope and operational
implications than are used in TI’s testing. Unit-level requirements should not be confused with reference design
testing that only validates the ruggedness of the TPS23757.
Layout
Printed circuit board layout recommendations are provided in the evaluation module (EVM) documentation
available for these devices.
Copyright ? 2009–2013, Texas Instruments Incorporated
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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