參數(shù)資料
型號(hào)： LTC4270AIUKG#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 模擬信號(hào)調(diào)理
英文描述： SPECIALTY ANALOG CIRCUIT, PQCC52
封裝： 8 X 7 MM, LEAD FREE, PLASTIC, QFN-52
文件頁(yè)數(shù)： 14/32頁(yè)
文件大?。?/td> 344K
代理商： LTC4270AIUKG#PBF
LTC4270/LTC4271
21
42701fa
the Port Status register will always report the results of the
last class pulse, so an invalid Class 4–Class 2 combination
would report a second class pulse was run in the High
Power Status register (which implies that the first cycle
found class 4), and Class 2 in the Port Status register.
POWER CONTROL
The primary function of the LTC4270/LTC4271 is to con-
trol the delivery of power to the PSE port. It does this by
controlling the gate drive voltage of an external power
MOSFET while monitoring the current via an external sense
resistor and the output voltage at the OUT pin. This circuitry
serves to couple the raw VEE input supply to the port in
a controlled manner that satisfies the PDs power needs
while minimizing both power dissipation in the MOSFET
and disturbances on the VEE backplane.
Inrush Control
Once the command has been given to turn on a port, the
LTC4270/LTC4271 ramps up the GATE pin of that port’s
external MOSFET in a controlled manner. Under normal
power-up circumstances, the MOSFET gate will rise until
the port current reaches the inrush current limit level
(typically 425mA), at which point the GATE pin will be
servoed to maintain the specified IINRUSH current. During
this inrush period, a timer (tSTART) runs. When output
charging is complete, the port current will fall and the GATE
pin will be allowed to continue rising to fully enhance the
MOSFET and minimize its on-resistance. The final VGS is
nominally 12V. The inrush period is maintained until the
tSTART timer expires. At this time if the inrush current limit
level is still exceeded, the port will be turned back off and
a tSTART fault reported.
Current Limit
Each LTC4270/LTC4271 port includes two current limiting
thresholds (ICUT and ILIM), each with a corresponding
timer (tCUT and tLIM). Setting the ICUT and ILIM thresholds
depends on several factors: the class of the PD, the volt-
APPLICATIONS INFORMATION
age of the main supply (VEE), the type of PSE (Type 1 or
Type 2), the sense resistor (0.5Ω or 0.25Ω), the SOA of
the MOSFET, and whether or not the system is required
to enforce class current levels.
Per the IEEE specification, the LTC4270/LTC4271 will al-
low the port current to exceed ICUT for a limited period of
time before removing power from the port, whereas it will
actively control the MOSFET gate drive to keep the port
current below ILIM. The port does not take any action to
limit the current when only the ICUT threshold is exceeded,
but does start the tCUT timer. If the current drops below
the ICUT current threshold before its timer expires, the
tCUT timer counts back down, but at 1/16 the rate that it
counts up. If the tCUT timer reaches 60ms (typical) the
port is turned off and the port tCUT fault is set. This allows
the current limit circuitry to tolerate intermittent overload
signals with duty cycles below about 6%; longer duty cycle
overloads will turn the port off.
The ILIM current limiting circuit is always enabled and ac-
tively limiting port current. The tLIM timer is enabled only
when the tLIM Enable bit is set. This allows tLIM to be set
to a shorter value than tCUT to provide more aggressive
MOSFET protection and turn off a port before MOSFET
damage can occur. The tLIM timer starts when the ILIM
threshold is exceeded. When the tLIM timer reaches 12ms
(typical) the port is turned off and the port tLIM fault is
set. When the tLIM Enable bit is disabled tLIM behaviors
are tracked by the tCUT timer, which counts up during both
ILIM and ICUT events.
ICUT is typically set to a lower value than ILIM to allow the
port to tolerate minor faults without current limiting.
Per the IEEE specification, the LTC4270/LTC4271 will au-
tomatically set ILIM to 425mA (shown in bold in Table 6)
during inrush at port turn-on, and then switch to the
programmed ILIM setting once inrush has completed. To
maintain IEEE compliance, ILIM should be kept at 425mA
for all Type 1 PDs, and 850mA if a Type 2 PD is detected.
ILIM is automatically reset to 425mA when a port turns off.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)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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