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| 型号： | LTC4257IS8#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/20页 |
| 文件大小： | 263K |
| 描述： | IC CTRLR INTFACE PWR/ETHER 8SOIC |
| 产品培训模块： | Power over Ethernet |
| 标准包装： | 100 |
| 类型： | 以太网供电开关（PoE） |
| 应用： | IP 电话，LAN 网络供电，网络路由器和交换机 |
| 内部开关： | 是 |
| 电流限制： | 350mA |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 8-SOIC |
| 包装： | 管件 |
| 产品目录页面： | 1338 (CN2011-ZH PDF) |
LTC4257
12
4257fb
EXTERNAL INTERFACE AND COMPONENT SELECTION
Transformer
Nodes on an Ethernet network commonly interface to the
outside world via an isolation transformer (Figure 8). For
powered devices, the isolation transformer must include
a center tap on the media (cable) side. Proper termination
is required around the transformer to provide correct
impedance matching and to avoid radiated and conducted
emissions. Transformer vendors such as Pulse, Bel Fuse,
Tyco and others (Table 3) can provide assistance with
selection of an appropriate isolation transformer and
proper termination methods. These vendors have trans-
formers specifically designed for use in PD applications.
Table 3. Power over Ethernet Transformer Vendors
VENDOR
CONTACT INFORMATION
Pulse Engineering
12220 World Trade Drive
San Diego, CA 92128
Tel: 858-674-8100
FAX: 858-674-8262
http://www.pulseeng.com/
Bel Fuse Inc.
206 Van Vorst Street
Jersey City, NJ 07302
Tel: 201-432-0463
FAX: 201-432-9542
http://www.belfuse.com/
Tyco Electronics
308 Constitution Drive
Menlo Park, CA 94025-1164
Tel: 800-227-7040
FAX: 650-361-2508
http://www.circuitprotection.com/
Diode Bridges
IEEE 802.3af allows power wiring in either of two configu-
rations on the TX/RX wires, plus power can be applied to
the PD via the spare wire pair in the RJ45 connector. The
PD is required to accept power in either polarity on both
the main and spare inputs, therefore it is common to install
diode bridges on both inputs in order to accommodate the
different wiring configurations. Figure 8 demonstrates an
implementation of these diode bridges. The specification
also mandates that the leakage back through the unused
bridge be less than 28礎 when the PD is powered with
57V.
The IEEE standard includes an AC impedance requirement
in order to implement the AC disconnect function. Capaci-
tor C14 in Figure 8 is used to meet this AC impedance
requirement. A 0.1礔 capacitor is recommended for this
application.
The LTC4257 has several different modes of operation
based on the voltage present between the V
IN
and GND
pins. The forward voltage drop of the input diodes in a PD
design subtracts from the input voltage and will affect the
transition point between modes. When using the LTC4257,
it is necessary to pay close attention to this forward
voltage drop. Selection of oversized diodes will help keep
the PD thresholds from exceeding IEEE specifications.
The input diode bridge of a PD can consume 4% of the
avialable power in some applications. It may be desirable
to use Scottky diodes in order to reduce this power loss.
APPLICATIO S I FOR ATIO
U
U
U
Figure 8. PD Front End with Isolation Transformer, Diode Bridges and Capacitor
16
14
15
1
3
2
RX
6
RX
+
3
TX
2
TX
+
RJ45
T1
PULSE H2019
4257 F08
1
7
8
5
4
11
9
10
6
8
7
D3
SMAJ58A
TVS
BR1
DF01SA
BR2
DF01SA
TO PHY
GND
8
5
4
LTC4257
C1
V
IN
V
OUT
V
OUT
SPARE
SPARE
+
C14
0.1礔
100V
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4258 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Quad IEEE 802.3at Power over Ethernet Controller |
| LTC4258_09 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Quad IEEE 802.3af Power over Ethernet Controller with Integrated Detection |
| LTC4258CGW | 制造商:Linear Technology 功能描述:POWER OVER ETHERNET CONTROLLER |
| LTC4258CGW#PBF | 功能描述:IC POE 802.3AF QUAD 36-SSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 控制器 系列:- 标准包装:2,450 系列:- 控制器类型:SPI 总线至 I²C 总线桥接 接口:I²C，串行，SPI 电源电压:2.4 V ~ 3.6 V 电流 - 电源:11mA 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:24-VFQFN 裸露焊盘 供应商设备封装:24-HVQFN（4x4） 包装:托盘 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名称:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4258CGW#TR | 制造商:Linear Technology 功能描述:POWER OVER ETHERNET CONTROLLER |
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