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參數資料
| 型號： | LTC4274CUHF#PBF |
| 廠商： | Linear Technology |
| 文件頁數： | 17/28頁 |
| 文件大小： | 702K |
| 描述： | IC CONTROLLER POE 38-QFN |
| 標準包裝： | 52 |
| 類型： | 以太網供電 PSE 控制器（PoE） |
| 應用： | 供電設備（PSE） |
| 內部開關： | 無 |
| 電流限制： | 可調 |
| 電源電壓： | 3 V ~ 4.3 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 38-QFN |
| 供應商設備封裝： | 38-QFN（5x7）裸露焊盤 |
| 包裝： | 管件 |
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LTC4274
17
4274fd
APPLICATIONS INFORMATION
DETECTION
Detection Overview
To avoid damaging network devices that were not designed
to tolerate DC voltage, a PSE must determine whether the
connected device is a real PD before applying power. The
IEEE specification requires that a valid PD have a common-
mode resistance of 25k ?% at any port voltage below
10V. The PSE must accept resistances that fall between
19k and 26.5k, and it must reject resistances above 33k
or below 15k (shaded regions in Figure 11). The PSE may
choose to accept or reject resistances in the undefined
areas between the must-accept and must-reject ranges. In
particular, the PSE must reject standard computer network
ports, many of which have 150?common-mode termina-
tion resistors that will be damaged if power is applied to
them (the black region at the left of Figure 11).
and short circuits, are also reported. If the port measures
less than 1V at the first forced-current test, the detection
cycle will abort and Short Circuit will be reported. Table 3
shows the possible detection results.
Table 3. Detection Status
MEASURED PD SIGNATURE
DETECTION RESULT
Incomplete or Not Yet Tested
Detect Status Unknown
<2.4k
Short Circuit
Capacitance > 2.7糉
C
PD
too High
2.4k < R
PD
< 17k
R
SIG
too Low
17k < R
PD
< 29k
Detect Good
>29k
R
SIG
too High
>50k
Open Circuit
Voltage > 10V
Port Voltage Outside Detect Range
Operating Modes
The ports operating mode determines when the LTC4274
runs a detection cycle. In manual mode, the port will
idle until the host orders a detect cycle. It will then run
detection, report the results, and return to idle to wait for
another command.
In semi-auto mode, the LTC4274 autonomously polls the
port for PDs, but it will not apply power until commanded
to do so by the host. The Port Status register is updated
at the end of each detection cycle. If a valid signature
resistance is detected and classification is enabled, the
port will classify the PD and report that result as well.
Figure 12. PD Detection
Figure 11. IEEE 802.3af Signature Resistance Ranges
4-Point Detection
The LTC4274 uses a 4-point detection method to discover
PDs. False-positive detections are minimized by check-
ing for signature resistance with both forced-current and
forced-voltage measurements. Initially, two test currents
are forced onto the port (via the OUT pin) and the resulting
voltages are measured. The detection circuitry subtracts
the two V-I points to determine the resistive slope while
removing offset caused by series diodes or leakage at
the port (see Figure 12). If the forced-current detection
yields a valid signature resistance, two test voltages are
then forced onto the port and the resulting currents are
measured and subtracted. Both methods must report valid
resistances for the port to report a valid detection. PD
signature resistances between 17k and 29k (typically) are
detected as valid and reported as Detect Good in the Port
Status register. Values outside this range, including open
RESISTANCE
PD
PSE
0?/DIV>
10k
15k
4274 F11
19k
26.5k
26.25k
23.75k
150?(NIC)
20k
30k
33k
FIRST
DETECTION
POINT
SECOND
DETECTION
POINT
VALID PD
25k?SLOPE
275
165
0V-2V
OFFSET
VOLTAGE
4274 F12
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相關代理商/技術參數 |
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| LTC4274IUHF#PBF | 制造商:Linear Technology 功能描述:POE Controller 25.5W 38-Pin QFN EP 制造商:Linear Technology 功能描述:Bulk 制造商:Linear Technology 功能描述:IC POE IEEE 802.3AT 38-QFN 制造商:Linear Technology 功能描述:IC POE CNTRL 38QFN 制造商:Linear Technology 功能描述:IC, POE, CNTRL, 38QFN 制造商:Linear Technology 功能描述:IC, POE CONTROLLER, 3.6V, QFN-38; Input Voltage:3.6V; Supply Current:1.1mA; Digital IC Case Style:QFN; No. of Pins:38; Frequency:1MHz; Operating Temperature Min:-40C; Operating Temperature Max:85C; MSL:MSL 1 - Unlimited ;RoHS Compliant: Yes |
| LTC4274IUHF#PBF | 制造商:Linear Technology 功能描述:IC POE CONTROLLER 3.6V QFN-38 |
| LTC4274IUHF#TRPBF | 制造商:Linear Technology 功能描述:POE Controller 25.5W 38-Pin QFN EP |
| LTC42766C | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Quad PoE/PoE/LTPoE PSE Controller |
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