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參數(shù)資料
| 型號： | LTC4258CGW#PBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 18/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC POE 802.3AF QUAD 36-SSOP |
| 產(chǎn)品培訓(xùn)模塊： | Power over Ethernet |
| 標(biāo)準(zhǔn)包裝： | 32 |
| 控制器類型： | 以太網(wǎng)供電控制器（POE） |
| 接口： | IEEE 802.3af |
| 電源電壓： | 3 V ~ 4 V |
| 電流 - 電源： | 2.5mA |
| 工作溫度： | 0°C ~ 70°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 36-BSOP（0.295"，7.50mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 36-SSOP |
| 包裝： | 管件 |
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LTC4258
25
4258fb
IEEE 802.3af COMPLIANCE AND EXTERNAL
COMPONENT SELECTION
The LTC4258 is designed to control power delivery in IEEE
802.3af compliant Power Sourcing Equipment (PSE).
Because proper operation of the LTC4258 may depend on
external signals and power sources, like the –48V supply
(VEE), external components such as the sense resistors
(RS), and possibly software running on an external micro-
processor, using the LTC4258 in a PSE does not guarantee
802.3af compliance. Using an LTC4258 does get you most
of the way there. This section discusses the rest of the
elements that go along with the LTC4258 to make an
802.3af complaint PSE. Each paragraph below addresses
a component which is critical for PSE compliance as well
as possible pitfalls that can cause a PSE to be noncompliant.
For further assistance please contact Linear Technology’s
Applications department.
Sense Resistors
The LTC4258 is designed to use a 0.5
sense resistor, RS,
to monitor the current through each port. The value of the
sense resistor has been minimized in order to reduce
power loss and as a consequence, the voltage which the
LTC4258 must measure is small. Each port may be draw-
ing up to 450mA with this current flowing through the
sense resistor and associated circuit board traces. To
prevent parasitic resistance on the circuit board from
obscuring the voltage drop across the sense resistor, the
LTC4258 must Kelvin sense the resistor voltage. One way
to achieve Kelvin sensing is “star grounding,” shown
pictorially in Figure 1. Another option is to use a – 48V
power plane to connect the sense resistor and the LTC4258
VEE pin. Either of these strategies will prevent voltages
developed across parasitic circuit board resistances from
affecting the LTC4258 current measurement accuracy.
The precision of the sense resistor directly affects the
measurement of the IEEE parameters IINRUSH, ILIM, ICUT
and IMIN. Therefore, to maintain IEEE compliance, use a
resistor with 0.5% or better accuracy.
Power MOSFETs
The LTC4258 controls power MOSFETs in order to regu-
late current flow through the Ethernet ports. Under certain
conditions these MOSFETs have to dissipate significant
power. See the Choosing External MOSFETs section for a
detailed discussion of the requirements these devices
must meet.
APPLICATIO S I FOR ATIO
WU
UU
VCC
100
H
10
H
B1100
ISOLATED
GND
ISOLATED
–48V
FMMT723
6
5
2
3
4
1
ITH/RUN
VFB
NGATE
LTC3803
SENSE
GND
10k
1k
3.32k
1%
0.100
1%
806
1%
47.5k
1%
4258 F16
56k
0.22
F
100V
10
F
63V
VEE
VDD
3.3V
400mA
10
F
6.3V
ISOLATED
GND
0.22
F
100V
100
F
6.3V
2200pF
+
FDC2512
10
F
16V
5
Figure 18. –48V to 3.3V Boost Converter
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| LTC4259ACGW | 功能描述:IC CTRLR POE QUAD AC DISC 36SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4259ACGW#PBF | 功能描述:IC CTRLR POE QUAD AC DISC 36SSOP RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4259ACGW#TR | 功能描述:IC CTRLR POE QUAD AC DISC 36SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
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