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參數(shù)資料
| 型號(hào)： | LTC4258CGW#TRPBF |
| 廠商： | Linear Technology |
| 文件頁(yè)數(shù)： | 13/28頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC POE 802.3AF QUAD 36-SSOP |
| 標(biāo)準(zhǔn)包裝： | 1,000 |
| 控制器類型： | 以太網(wǎng)供電控制器（POE） |
| 接口： | IEEE 802.3af |
| 電源電壓： | 3 V ~ 4 V |
| 電流 - 電源： | 2.5mA |
| 工作溫度： | 0°C ~ 70°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 36-BSOP（0.295"，7.50mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 36-SSOP |
| 包裝： | 帶卷 (TR) |
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LTC4258
20
4258fb
APPLICATIO S I FOR ATIO
WU
UU
current in the cable from increasing too quickly and the
LTC4258’s built-in short-circuit protection will take con-
trol of the situation and turn off the port. Some energy is
stored in the cable, but the transient suppressor on the
port clamps the port voltage when the cable inductance
causes the voltage to fly back after the MOSFET is turned
off. Because the cable only had 600mA or so going through
it, an SMAJ58A or equivalent device can easily control the
port voltage during flyback. With no cable connected at all,
a powered port shorted at the PSE’s RJ-45 connector can
reach high current levels before the port is shut down. There
is no cable inductance to store energy so once the port is
shut down the situation is under control.
A short—hence low inductance—piece of CAT-5 will not
limit the rapid increase of current when the port is shorted.
Even though the LTC4258 short-circuit shutdown is fast,
the cable may have many amps flowing through it before
the MOSFET can be turned off. Due to the high current,
this short piece of cable flies back with significant energy
behind it and must be controlled by the transient suppres-
sor. Choosing a surge suppressor that will not develop
more than a few volts of forward voltage while passing
more than 10A is important. A positive port voltage may
forward bias the detect diode (DDETn), bringing the
LTC4258’s DETECT
n pin positive as well and engaging
the DETECT
n clamps. This will generally not damage the
LTC4258 but extreme cases can cause the LTC4258 to
reset. When it resets, the LTC4258 signals an interrupt,
alerting the host controller which can then return the
LTC4258 to normal operating mode.
A substantial transient surge suppressor can typically
protect the LTC4258 and the rest of the PSE from these
faults. Placing a polyfuse between the RJ-45 connector
and the LTC4258 and its associated circuitry can provide
additional protection. To meet safety requirements, place
the polyfuse in the ground leg of the PSE’s output.
DC DISCONNECT
DC disconnect monitors the sense resistor voltage when-
ever the power is on to make sure that the PD is drawing
the minimum specified current. The disconnect timer
counts up whenever port current is below 7.5mA (typ). If
the tDIS timer runs out, the corresponding port will be
turned off and the disconnect bit in the fault register will be
set. If the undercurrent condition goes away before the
tDIS timer runs out, the timer will reset. The timer will start
counting from the beginning if the undercurrent condition
occurs again. The undercurrent circuit includes a glitch
filter to filter out noise.
The DC disconnect feature can be disabled by clearing the
corresponding DC Discon Enable bits in the Disconnect
register (13h). The tDIS timer duration can be programmed
by bits 1 and 0 of register 16h.
The LTC4258 implements a variety of current sense and
limit thresholds to control current flowing through the
port. Figure 16 is a graphical representation of these
thresholds and the action the LTC4258 takes when
currrent crosses the thresholds.
Figure 16. LTC4258 Current Sense and Limits
0mA
0mV
100mA
CURRENT
RS = 0.5
DC DIS-
CONNECT
CUT
(ICUT)
LIMIT
(ILIM)
SHORT
CIRCUIT
EFFECT
SENSE
n
VOLTAGE
50mV
200mA
100mV
300mA
150mV
400mA
200mV
500mA
250mV
600mA
300mV
CURRENT
LIMIT
PORT OFF IN tICUT
OR tSTART
CURRENT LIMIT
IN 1
s
NORMAL
OPERATION
PORT OFF IN tDIS
4258 F14
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| LTC4259ACGW | 功能描述:IC CTRLR POE QUAD AC DISC 36SSOP RoHS:否 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤(pán) 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤(pán) 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4259ACGW#PBF | 功能描述:IC CTRLR POE QUAD AC DISC 36SSOP RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標(biāo)準(zhǔn)包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤(pán) 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤(pán) 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
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