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TPS23757
SLVS948D – JULY 2009 – REVISED NOVEMBER 2013
www.ti.com
Inrush and Startup
The TPS23757 provides a 140 mA inrush limit that is compatible with both type 1 and type 2 PSEs. The
TPS23757’s internal softstart permits control of the converter startup preventing the converter from exceeding the
PSE output limitations. APb becomes valid within t APb after converter switching starts, or if an adapter is plugged
in while the PD is operating from a PSE.
Maintain Power Signature
The MPS is an electrical signature presented by the PD to assure the PSE that it is still present after operating
voltage is applied. A valid MPS consists of a minimum dc current of 10 mA (or a 10 mA pulsed current for at
least 75 ms every 325 ms) and an ac impedance lower than 26.3 k ? in parallel with 0.05 μ F. The ac impedance
is usually accomplished by the minimum operating C IN requirement of 5 μ F. When either APD or DEN is used to
force the hotswap switch off, the dc MPS will not be met. A PSE that monitors the dc MPS will remove power
from the PD when this occurs. A PSE that monitors only the ac MPS may remove power from the PD.
Startup and Converter Operation
The internal PoE UVLO (Under Voltage Lock Out) circuit holds the hotswap switch off before the PSE provides
full voltage to the PD. This prevents the converter circuits from loading the PoE input during detection and
classification. The converter circuits will discharge C IN , C VC , and C VB while the PD is unpowered. Thus V VDD -V RTN
will be a small voltage just after full voltage is applied to the PD, as seen in Figure 20 . The PSE drives the PI
voltage to the operating range once it has decided to power up the PD. When V VDD rises above the UVLO turn-
on threshold (V UVLO-R , ~35 V) with RTN high, the TPS23757 enables the hotswap MOSFET with a ~140 mA
(inrush) current limit as seen in Figure 21 . Converter switching is disabled while C IN charges and V RTN falls from
V VDD to nearly V VSS , however the converter startup circuit is allowed to charge C VC (the bootstrap startup
capacitor). Additional loading applied between V VDD and V RTN during the inrush state may prevent successful PD
and subsequent converter start up. Converter switching is allowed if the PD is not in inrush, converter OTSD
(over-temperature shutdown) is not active, and the V C UVLO permits it. Once the inrush current falls about 10%
below the inrush current limit, the PD current limit switches to the operational level (~450 mA). Continuing the
startup sequence shown in Figure 21 , V VC continues to rise until the startup threshold (V CUV , ~9 V) is exceeded,
turning the startup source off and enabling switching. The V B regulator is always active, powering the internal
converter circuits as V VC rises. There is a slight delay between the removal of charge current and the start of
switching as the softstart ramp sweeps above the V ZDC threshold. V VC falls as it powers both the internal circuits
and the switching MOSFET gates. If the converter control bias output rises to support V VC before it falls to V CUV –
V CUVH ( ~5.5 V), a successful startup occurs. APb in Figure 21 becomes active within t APb from the start of
switching, indicating that an adapter is plugged in.
V APb RTN
10 V/div
100 mA/div
10 V/div
2 V/div
50 V/div
-V
I PI
V VC - V RTN
V OUT
V VDD - V RTN
Inrush
PI Powered
Switching Starts
t - Time - 10 ms/div
Figure 21. Power Up and Start
18
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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