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参数资料
| 型号： | LTC4257CS8-1#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 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： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SO-8 |
| 文件页数： | 17/20页 |
| 文件大小： | 265K |
| 代理商： | LTC4257CS8-1#PBF |
LTC4257-1
6
42571fb
The LTC4257-1 is intended for use as the front end of a
Powered Device (PD) adhering to the IEEE 802.3af standard.
The LTC4257-1 includes a trimmed 25k signature resistor,
classification current source, and an input current limit cir-
cuit. With these functions integrated into the LTC4257-1,
the signature and power interface for a PD that meets all
the requirements of the IEEE 802.3af specification can be
built with a minimum of external components.
The LTC4257-1 has been specifically designed to interface
with legacy PoE PSEs which do not meet the inrush
current requirement of the IEEE 802.3af specification. By
setting the initial inrush current limit to a low level, a PD
using the LTC4257-1 minimizes the current drawn from
the PSE during start-up. After powering up, the LTC4257-1
switches to the high level current limit, thereby allowing
the PD to consume up to 12.95 watts if an 802.3af PSE is
present. This low level current limit also allows the
LTC4257-1 to charge arbitrarily large load capacitors
without exceeding the inrush limits of the IEEE 802.3af
specification. This dual level current limit provides the
system designer with flexibility to design PDs which are
compatible with legacy PSEs while also being able to take
advantage of the higher power allocation available in an
IEEE 802.3af system.
Using an LTC4257-1 for the power and signature inter-
face functions of a PD provides several advantages. The
LTC4257-1 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 inrush current limit
requirement of the IEEE 802.3af standard causes large
transient power dissipation in the PD. The LTC4257-1 is
designed to allow multiple turn-on sequences without
overheating the miniature 8-lead package. In the event of
excessive power cycling, the LTC4257-1 provides ther-
mal overload protection to keep the onboard power
MOSFET within its safe operating area.
Operation
The LTC4257-1 has several modes of operation depend-
ing on the applied input voltage as shown in Figure 1 and
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, ILOAD
CURRENT
LIMIT, ILIMIT
42571 F01
ICLASS DEPENDENT ON RCLASS SELECTION
ILIMIT = 140mA (NOMINAL)
I1 =
V1 – 2 DIODE DROPS
25k
ILOAD =
VIN
RLOAD
I2 =
V2 – 2 DIODE DROPS
25k
GND
2
PSE
IIN
LTC4257-1
8
6
5
R9
RLOAD
RCLASS
VOUT
C1
GND
4
RCLASS
PWRGD
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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相关PDF资料 |
PDF描述 |
|---|---|
| LTC4257CS8-1#TRPBF | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: 0°C to +70°C |
| LTC4257IDD-1#PBF | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: DFN; No of Pins: 8; Temperature Range: -40°C to +85°C |
| LTC4257IDD-1#TRPBF | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: DFN; No of Pins: 8; Temperature Range: -40°C to +85°C |
| LTC4257IS8-1#PBF | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: -40°C to +85°C |
| LTC4257IS8-1#TRPBF | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: -40°C to +85°C |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4257IDD | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4257IDD#PBF | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4257IDD#TR | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4257IDD#TRPBF | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4257IDD-1 | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
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