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參數資料
| 型號： | LTC4257CS8#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 網絡接口 |
| 英文描述： | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: 0°C to +70°C |
| 中文描述： | DATACOM, NETWORK INTERFACE SUPPORT CIRCUIT, PDSO8 |
| 封裝： | 0.150 INCH, LEAD FREE, PLASTIC, SOP-8 |
| 文件頁數： | 17/20頁 |
| 文件大小： | 258K |
| 代理商： | LTC4257CS8#TRPBF |
LTC4257
6
4257fb
The LTC4257 is intended for use as the front end of a
Powered Device (PD) designed to IEEE 802.3af draft
standard. The LTC4257 includes a trimmed 25k signature
resistor, classification current source, and an inrush cur-
rent limit circuit. With these functions integrated into the
LTC4257, the signature and power interface for a PD that
meets all the requirements of IEEE 802.3af can be built
with a minimum of external components.
Using an LTC4257 for the power and signature interface
functions of a PD provides several advantages. The
LTC4257 current limit circuit includes an onboard, 100V,
400mA power MOSFET with low leakage. This onboard
low leakage MOSFET avoids the possibility of corrupting
the 25k signature resistor while also saving board space
and cost. In addition, the IEEE 802.3af inrush current limit
requirement causes large transient power dissipation in
the PD; the LTC4257 manages this turn-on sequence
through the use of smart thermal protection circuitry. The
LTC4257 is designed to allow multiple turn-on sequences
without overheating the miniature 8-lead package. In the
event of excessive power cycling, the LTC4257 provides
thermally activated current-limit reduction to keep the
onboard power MOSFET within its safe operating area.
Operation
The LTC4257 has several modes of operation depending
on the applied input voltage as shown in Figure 1 and
summarized in Table 1. These various modes satisfy the
requirements defined in the IEEE 802.3af specification.
The input voltage is applied to the VIN pin and is with
reference to the GND pin. This input voltage is always
negative. To avoid confusion, voltages in this data sheet
are always referred to in terms of absolute magnitude.
Terms such as
maximum negative voltage refer to the
largest negative voltage and a
rising negative voltage
refers to a voltage that is becoming more negative. Refer-
ences to electrical parameters in this applications section
use the nominal value. Refer to the Electrical Characteris-
tics section for the range of values a particular parameter
will have.
DETECTION V1
CLASSIFICATION
UVLO
TURN-ON
UVLO
OFF
POWER
BAD
UVLO
OFF
UVLO
ON
UVLO
TURN-OFF
τ = RLOAD C1
PWRGD TRACKS
VIN
DETECTION V2
–10
TIME
–20
–30
V
IN
(V)
–40
–50
–10
TIME
–20
–30
V
OUT
(V)
–40
–50
–10
TIME
–20
–30
PWRGD
(V)
–40
–50
ICLASS
PD
CURRENT
ILIMIT
dV
dt
ILIMIT
C1
=
POWER
BAD
POWER
GOOD
DETECTION I1
CLASSIFICATION
ICLASS
DETECTION I2
LOAD CURRENT, ILOAD
CURRENT
LIMIT, ILIMIT
4257 F01
ICLASS DEPENDENT ON RCLASS SELECTION
ILIMIT = 350mA (NOMINAL)
I1 =
V1 – 2 DIODE DROPS
25k
ILOAD =
VIN
RLOAD
I2 =
V2 – 2 DIODE DROPS
25k
GND
2
PSE
IIN
8
6
5
R9
RLOAD
RCLASS
VOUT
C1
GND
4
RCLASS
PWRGD
LTC4257
VOUT
VIN
Figure 1. Output Voltage, PWRGD and PD Current
as a Function of Input Voltage
APPLICATIO S I FOR ATIO
WU
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相關代理商/技術參數 |
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| LTC4257IDD | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:10-MSOP 包裝:管件 |
| LTC4257IDD#PBF | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:10-MSOP 包裝:管件 |
| LTC4257IDD#TR | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:10-MSOP 包裝:管件 |
| LTC4257IDD#TRPBF | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:10-MSOP 包裝:管件 |
| LTC4257IDD-1 | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應商設備封裝:10-MSOP 包裝:管件 |
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