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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： | 2/20页 |
| 文件大小： | 265K |
| 代理商： | LTC4257CS8-1#PBF |
LTC4257-1
10
42571fb
Undervoltage Lockout
The IEEE specification dictates a maximum turn-on volt-
age of 42V and a minimum turn-off voltage of 30V for the
PD. In addition, the PD must maintain large on-off hyster-
esis to prevent resistive losses in the wiring between the
PSE and the PD from causing start-up oscillation. The
LTC4257-1 incorporates an undervoltage lockout (UVLO)
circuit that monitors line voltage to determine when to
apply power to the PD load (Figure 6). Before power is
applied to the load, the VOUT pin is high impedance and
sitting at ground potential since there is no charge on
capacitor C1. When the input voltage rises above the UVLO
turn-on threshold, the LTC4257-1 removes the classifica-
tion load current and turns on the internal power MOSFET.
C1 charges up under LTC4257-1 current limit control and
the VOUT pin transitions from 0V to VIN. This sequence is
shown in Figure 1. The LTC4257-1 includes a hysteretic
UVLO circuit that keeps power applied to the load until the
input voltage falls below the UVLO turn-off threshold.
Once the input voltage drops below –30V, the internal
power MOSFET is turned off and the classification load
current is re-enabled. C1 will discharge through the PD
circuitry and the VOUT pin will go to a high impedance state.
Input Current Limit
IEEE 802.3af specifies a maximum inrush current and also
specifies a minimum load capacitor between the GND and
VOUT pins. To control turn-on surge current in the system,
the LTC4257-1 integrates a dual level current limit circuit
with an onboard power MOSFET and sense resistor to
provide a complete inrush control circuit without additional
external components. At turn on, the LTC4257-1 will limit
input current to the low level, allowing the load capacitor
to ramp up to the line voltage in a controlled manner.
The LTC4257-1 has been specifically designed to interface
with legacy PSEs which do not meet the inrush current
requirement of the IEEE 802.3af specification. This is
APPLICATIO S I FOR ATIO
WU
UU
GND
C1
5
F
MIN
VIN
8
4
VOUT 5
LTC4257-1
42571 F06
TO
PSE
UNDERVOLTAGE
LOCKOUT
CIRCUIT
PD
LOAD
CURRENT-LIMITED
TURN ON
+
INPUT
LTC4257-1
VOLTAGE
POWER MOSFET
0V TO UVLO*
OFF
>UVLO*
ON
*UVLO INCLUDES HYSTERESIS
RISING INPUT THRESHOLD
–36V
FALLING INPUT THRESHOLD
–30.5V
Figure 6. LTC4257-1 Undervoltage Lockout
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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