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| 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： | 3/20页 |
| 文件大小： | 265K |
| 代理商： | LTC4257CS8-1#PBF |
LTC4257-1
11
42571fb
accomplished by a dual level current limit. At turn on
before C1 is charged, the LTC4257-1 current limit is set to
the low level. After C1 is charged up and the VOUT – VIN
voltage difference is below the power good threshold, the
LTC4257-1 switches to the high level current limit. The
dual level current limit allows legacy PSEs with limited
current sourcing capability to power up the PD while also
allowing the PD to draw full power from an IEEE 802.3af
PSE.
The dual level current limit also allows use of arbitrarily
large load capacitors. The IEEE 802.3af specification man-
dates that at turn on the PD not exceed the inrush current
limit for more than 50ms. The LTC4257-1 is not restricted
by the 50ms time limit because the load capacitor is
charged with a current below the IEEE inrush current limit
specification. Therefore, it is possible to use larger load
capacitors with the LTC4257-1.
As the LTC4257-1 switches from the low to the high level
current limit, a momenatry increase in current can be
observed. This current spike is a result of the LTC4257-1
charging the last 1.5V at the high level current limit. When
charging a 10
F capacitor, the current spike is typically
100
s wide and 125% of the nominal low level current
limit.
The LTC4257-1 stays in the high level current limit mode
until the input voltage drops below the UVLO turn-off
threshold. This dual level current limit provides the sys-
tem designer with the 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.
During the current limited turn on, a large amount of power
is dissipated in the power MOSFET. The LTC4257-1 is
designed to accept this thermal load and is thermally
protected to avoid damage to the onboard power MOSFET.
Note that in order to adhere to the IEEE 802.3af standard,
it is necessary for the PD designer to ensure the PD steady-
state power consumption falls within the limits shown in
Table 2.
Power Good
The LTC4257-1 includes a power good circuit (Figure 7)
that is used to indicate to the PD circuitry that load
capacitor C1 is fully charged and that the PD can start
DC/DC converter operation. The power good circuit moni-
tors the voltage across the internal power MOSFET and
PWRGD is asserted when the voltage drops below 1.5V.
The power good circuit includes a large amount of hyster-
esis to allow the LTC4257-1 to operate near the current
limit point without inadvertently disabling PWRGD. The
MOSFET voltage must increase to 3V before PWRGD is
disabled.
APPLICATIO S I FOR ATIO
WU
UU
Figure 7. LTC4257-1 Power Good
PWRGD
C1
5
F
MIN
VIN
6
4
VOUT
1.125V
300k
R9
100k
5
LTC4257-1
THERMAL SHUTDOWN
UVLO
42571 F07
TO
PSE
PD
LOAD
SHDN
+
–
+
–
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 |
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| 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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