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参数资料
| 型号： | LTC4270AIUKG#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 模拟信号调理 |
| 英文描述： | SPECIALTY ANALOG CIRCUIT, PQCC52 |
| 封装： | 8 X 7 MM, LEAD FREE, PLASTIC, QFN-52 |
| 文件页数： | 10/32页 |
| 文件大小： | 344K |
| 代理商： | LTC4270AIUKG#PBF |
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LTC4270/LTC4271
18
42701fa
Reset and the AUTO/MID Pins
The initial LTC4270/LTC4271 configuration depends on the
state of the AUTO and MID pins during reset. Reset occurs
at power-up, or whenever the RESET pin is pulled low or
the global Reset All bit is set. Note that the AUTO pin is
only sampled when a reset occurs. Changing the state of
AUTO or MID after power-up will not properly change the
port behavior of the LTC4270/LTC4271 until a reset occurs.
Although typically used with a host controller, the LTC4270/
LTC4271 can also be used in a standalone mode with no
connection to the serial interface. If there is no host pres-
ent, the AUTO pin should be tied high so that, at reset, all
ports will be configured to operate automatically. Each port
will detect and classify repeatedly until a PD is discovered,
set ICUT and ILIM according to the classification results,
apply power to valid PDs, and remove power when a PD
is disconnected.
Table 3 shows the ICUT and ILIM values that will be auto-
matically set in standalone (AUTO pin) mode, based on
the discovered class.
Table 3. ICUT and ILIM Values in Standalone Mode
CLASS
ICUT
ILIM
Class 1
112mA
425mA
Class 2
206mA
425mA
Class 3 or 0
375mA
425mA
Class 4
638mA
850mA
The automatic setting of ICUT and ILIM values only occurs
if the LTC4270/LTC4271 is reset with the AUTO pin high.
If the standalone application is a midspan, the MID pin
should be tied high to enable correct midspan detection
timing.
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-
APPLICATIONS INFORMATION
RESISTANCE
PD
PSE
0Ω
10k
15k
42701 F11
19k
26.5k
26.25k
23.75k
150Ω (NIC)
20k
30k
33k
Figure 11. IEEE 802.3af Signature Resistance Ranges
mode resistance of 25k ±5% 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 150Ω common-mode termination resistors
that will be damaged if power is applied to them (the black
region at the left of Figure 11).
4-Point Detection
The LTC4270/LTC4271 uses a 4-point detection method to
discover PDs. False-positive detections are minimized by
checking for signature resistance with both forced-current
and forced-voltage measurements.
Initially, two test currents are forced onto the port (via the
OUTn 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 result-
ing 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 corresponding Port Status register. Values
outside this range, including open 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 4 shows the possible
detection results.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4270BIUKG#PBF | 制造商:Linear Technology 功能描述:POE Controller 25.5W 52-Pin QFN EP 制造商:Linear Technology 功能描述:Bulk 制造商:Linear Technology 功能描述:IC POE LTPOE 12-PORT PSE 52-QFN 制造商:Linear Technology 功能描述:IC PSE CONTROLLER 3.3V QFN-52 制造商:Linear Technology 功能描述:PSE CNTRL 12 PORT 25.5W 1M 制造商:Linear Technology 功能描述:IC, PSE CONTROLLER, 3.3V, QFN-52; Input Voltage:3.3V; Supply Current:10mA; UVLO:25V; Digital IC Case Style:QFN; No. of Pins:52; Frequency:1MHz; Operating Temperature Min:-40C; Operating Temperature Max:85C; Package / Case:52-QFN ;RoHS Compliant: Yes |
| LTC4270BIUKG#PBF | 制造商:Linear Technology 功能描述:IC, PSE CONTROLLER, 3.3V, QFN-52 |
| LTC4270BIUKG#TRPBF | 制造商:Linear Technology 功能描述:POE Controller 25.5W 52-Pin QFN EP 制造商:Linear Technology 功能描述:PSE CONTROLLER, 12PORT, 57V, QFN-52; Supply Current:10mA; UVLO:25V; Digital IC Case Style:QFN; No. of Pins:52; Duty Cycle (%):6.3%; Frequency:1MHz; Operating Temperature Min:-40C; Operating Temperature Max:85C ;RoHS Compliant: Yes |
| LTC4270CIUKG#PBF | 制造商:Linear Technology 功能描述:POE Controller 13W 52-Pin QFN EP 制造商:Linear Technology 功能描述:IC POE LTPOE 12-PORT PSE 52-QFN 制造商:Linear Technology 功能描述:PSE CNTRL 12 PORT 13W 1MHZ 制造商:Linear Technology 功能描述:IC PSE CONTROLLER 3.3V QFN-52 制造商:Linear Technology 功能描述:IC, PSE CONTROLLER, 3.3V, QFN-52; Input Voltage:3.3V; Supply Current:10mA; UVLO:25V; Digital IC Case Style:QFN; No. of Pins:52; Frequency:1MHz; Operating Temperature Min:-40C; Operating Temperature Max:85C; Package / Case:52-QFN ;RoHS Compliant: Yes |
| LTC4270CIUKG#PBF | 制造商:Linear Technology 功能描述:IC PSE CONTROLLER 3.3V QFN-52 制造商:Linear Technology 功能描述:IC, PSE CONTROLLER, 3.3V, QFN-52 |
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