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参数资料
| 型号： | LTC4274AIUHF-2#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | POWER SUPPLY MANAGEMENT CKT, PQCC38 |
| 封装： | 7 X 5 MM, LEAD FREE, PLASTIC, MO-220WHKD, QFN-38 |
| 文件页数： | 11/28页 |
| 文件大小： | 313K |
| 代理商： | LTC4274AIUHF-2#TRPBF |
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LTC4274A/LTC4274C
19
4274acf
ApplicAtions inForMAtion
BehaviorinAUTOpinmodeissimilartosemi-auto;however,
after Detect Good is reported and the port is classified (if
classification is enabled), it is automatically powered on
without further intervention. In standalone (AUTO pin)
mode, the ICUT and ILIM thresholds are automatically set;
see the Reset and the AUTO/MID Pin section for more
information.
The signature detection circuitry is disabled when the port
is initially powered up with the AUTO pin low, in shutdown
mode, or when the corresponding Detect Enable bit is
cleared.
Detection of Legacy PDs
Proprietary PDs that predate the original IEEE 802.3af
standard are commonly referred to today as legacy de-
vices. One type of legacy PD uses a large common mode
capacitance (>10μF) as the detection signature. Note that
PDs in this range of capacitance are defined as invalid, so
a PSE that detects legacy PDs is technically noncompliant
with the IEEE spec.
The LTC4274A/LTC4274C can be configured to detect this
type of legacy PD. Legacy detection is disabled by default,
but can be manually enabled. When enabled, the port will
report Detect Good when it sees either a valid IEEE PD or
a high-capacitance legacy PD. With legacy mode disabled,
only valid IEEE PDs will be recognized.
CLASSIFICATION
802.3af Classification
A PD can optionally present a classification signature to
the PSE to indicate the maximum power it will draw while
operating. The IEEE specification defines this signature as
a constant current draw when the PSE port voltage is in the
VCLASS range (between 15.5V and 20.5V), with the current
level indicating one of 5 possible PD classes. Figure 13
shows a typical PD load line, starting with the slope of the
25k signature resistor below 10V, then transitioning to
the classification signature current (in this case, Class 3)
in the VCLASS range. Table 4 shows the possible clas-
sification values.
Table 4. Classification Values
CLASS
RESULT
Class 0
No Class Signature Present; Treat Like Class 3
Class 1
3W
Class 2
7W
Class 3
13W
Class 4
25.5W (Type 2)
If classification is enabled, the port will classify the PD
immediatelyafterasuccessfuldetectioncycleinsemi-auto
or AUTO pin modes, or when commanded to in manual
mode. It measures the PD classification signature by ap-
plying 18V for 12ms (both values typical) to the port via
the OUT pin and measuring the resulting current; it then
reports the discovered class in the Port Status register.
If the LTC4274A/LTC4274C is in AUTO pin mode, it will
additionally use the classification result to set the ICUT
and ILIM thresholds. See the Reset and the AUTO/MID Pin
section for more information.
The classification circuitry is disabled when the port is
initially powered up with the AUTO pin low, in shutdown
mode, or when the corresponding Class Enable bit is
cleared.
Figure 13. PD Classification
VOLTAGE (VCLASS)
0
CURRENT
(mA)
60
50
40
30
20
10
0
5
10
15
20
4274AC F13
25
TYPICAL
CLASS 3
PD LOAD
LINE
48mA
33mA
PSE LOAD LINE
23mA
14.5mA
6.5mA
CLASS 4
CLASS 2
CLASS 1
CLASS 0
CLASS 3
OVER
CURRENT
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| LTC4274AIUHF-4#PBF | 功能描述:IC CONTROLLER POE 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:119 系列:- 类型:热交换控制器 应用:通用型，PCI Express? 内部开关:无 电流限制:- 电源电压:3.3V，12V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:80-TQFP 供应商设备封装:80-TQFP（12x12） 包装:托盘 产品目录页面:1423 (CN2011-ZH PDF) |
| LTC4274AIUHF-4#TRPBF | 功能描述:IC CONTROLLER POE 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:119 系列:- 类型:热交换控制器 应用:通用型，PCI Express? 内部开关:无 电流限制:- 电源电压:3.3V，12V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:80-TQFP 供应商设备封装:80-TQFP（12x12） 包装:托盘 产品目录页面:1423 (CN2011-ZH PDF) |
| LTC4274C | 制造商:LINER 制造商全称:Linear Technology 功能描述:12-Port PoE/PoE+/LTPoE++ PSE Controller |
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