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參數(shù)資料
| 型號： | LTC4259ACGW#TR |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 21/32頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC CTRLR POE QUAD AC DISC 36SSOP |
| 標準包裝： | 1,000 |
| 控制器類型： | 以太網(wǎng)供電控制器（POE） |
| 接口： | I²C |
| 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） |
| 供應商設備封裝： | 36-SSOP |
| 包裝： | 帶卷 (TR) |
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LTC4259A
28
4259afb
components such as the sense resistors (RS), and possi-
bly software running on an external microprocessor,
using the LTC4259A in a PSE does not guarantee 802.3af
compliance. Using an LTC4259A does get you most of the
way there. This section discusses the rest of the elements
that go along with the LTC4259A to make an 802.3af
complaint PSE. Each paragraph below addresses a com-
ponent 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 LTC4259A 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
LTC4259A must measure is small. Each port may be
drawing 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
LTC4259A 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
LTC4259A VEE pin. Either of these strategies will prevent
voltages developed across parasitic circuit board resis-
tances from affecting the LTC4259A current measure-
ment accuracy. The precision of the sense resistor directly
affects the measurement of the IEEE parameters IINRUSH,
ILIM, ICUT and IMIN. Therefore, to maintain IEEE compli-
ance, use a resistor with 0.5% or better accuracy.
Power MOSFETs
The LTC4259A controls power MOSFETs in order to
regulate current flow through the Ethernet ports. Under
certain conditions these MOSFETs have to dissipate sig-
nificant power. See the Choosing External MOSFETs sec-
tion for a detailed discussion of the requirements these
devices must meet.
Common Mode Chokes
Both nonpowered and powered Ethernet connections
achieve best performance (for data transfer, power trans-
fer and EMI) when a common mode choke is used on each
port. In the name of cost reduction, some designs share a
common mode choke between two adjacent ports. Even
for nonpowered Ethernet, sharing a choke is not recom-
mended. With two ports passing through the choke, it
cannot limit the common mode current of either port.
Instead, the choke only controls the sum of both ports’
common mode current. Because cabling from the ports
generally connects to different devices up to 200m apart,
APPLICATIO S I FOR ATIO
WU
UU
DRV
100
100
H
4.7
H
B1100
10
F
16V
4700pF
100pF
CMPZ4702B
ISOLATED
GND
ISOLATED
–48V
Si2328DS
FMMT593
87
6
5
2
3
4
1
GATE
VIN
VC
S/S
SENSE
LT1619
FB
GND
Si2328DS
510
47k
3.32k
1%
0.100
1%
1W
1.24k
1%
100k
4259A F21
910k
1
F
100V
+
VEE
10
47
F
10V
VDD
3.3V
300mA
+
47
F
10V
ISOLATED
GND
+
Figure 21. –48V to 3.3V Boost Converter
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| LTC4259AIGW-1 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Quad IEEE 802.3af Power over Ethernet Controller with AC Disconnect |
| LTC4259AIGW-1#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:- 標準包裝: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 供應商設備封裝: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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