參數(shù)資料
型號(hào)： LTC4259ACGW
廠商： LINEAR TECHNOLOGY CORP
元件分類： 電源管理
英文描述： Quad IEEE 802.3af Power over Ethernet Controller with AC Disconnect
中文描述： 4-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO36
封裝： 0.300 INCH, PLASTIC, SSOP-36
文件頁(yè)數(shù)： 20/32頁(yè)
文件大?。?/td> 326K
代理商： LTC4259ACGW
LTC4259A
20
4259Af
The LTC4259A implements a variety of current sense and
limit thresholds to control current flowing through the
port. Figure 15 is a graphical representation of these
thresholds and the action the LTC4259A takes when
currrent crosses the thresholds.
AC DISCONNECT
AC disconnect is an alternate method of sensing the pres-
ence or absence of a PD by monitoring the port impedance.
The LTC4259A forces a signal, amplified from the OSCIN
pin, out of the DETECT pins and onto the Power over Eth-
ernet connection. It calculates the connection impedance
from ohm’s law, Z
PORT
= V
AC
/I
AC
. Like DC disconnect, the
AC disconnect sensing circuitry controls the disconnect
timer. When the connection impedance rises (AC current
falls below I
ACDMIN
) due to the removal of the PD, the dis-
connect timer counts up. If the impedance remains high
(AC current remains below I
ACDMIN
), the disconnect timer
counts to t
DIS
, the port is turned off and the port’s discon-
nect bit in the Fault Register is set. If the impedance falls
(AC current rises above I
ACDMIN
) before the maximum
count of the disconnect timer, the timer resets and the port
remains powered.
Like DC disconnect, AC disconnect can also be disabled by
clearing the corresponding AC Discon Enable bits in the
Disconnect register (13h). AC disconnect is also affected
by the t
DIS
duration programmed in register 16h.
Unlike DC disconnect, AC disconnect has no continuous
time output to the timer. Rather, AC disconnect will reset
the timer once every cycle, 1/f
OSCIN
, of the OSCIN signal if
the port draws more than I
ACDMIN
during that period.
Because of this behavior, the time to turn off the port after
PD removal, t
DIS
, may vary by up to one cycle of OSCIN
(1/f
OSCIN
) from the delay programmed with the t
DIS1
and
t
DIS0
bits. Note that AC disconnect and DC disconnect
signals that reset the t
DIS
timer are ORed together. Thus on
a port where both disconnect modes are enabled, either
disconnect sensing method can keep the port
powered even if the other reports that there is no PD
connected.
The AC disconnect circuitry senses the port and Power
over Ethernet connection from the DETECT pins. Connect
a 0.47
μ
F 100V X7R capacitor (C
DET
) and a 1k resistor
(R
DET
) from the port’s DETECT pin to the port’s output as
shown in Figure 16. This provides an AC path for sensing
the port impedance. The 1k resistor, R
DET
, limits current
flowing through this path during port power on and power
off.
Sizing of capacitors is critical to ensure proper function of
AC disconnect. C
PSE
(Figure 16) controls the connection
impedance on the PSE side. Its capacitance must be kept
low enough for AC disconnect to be able to sense the PD.
For operation near 100Hz, use a C
PSE
of 0.1
μ
F. On the
other hand, C
DET
has to be large enough to pass the signal
at the frequency of OSCIN. For f
OSCIN
≈
100Hz, use at least
a 0.47
μ
F 100V X7R capacitor. The sizes of C
PSE
, C
DET
,
R
DET
and the frequency, f
OSCIN
, are chosen to create an
economical, physically compact and functionally
ro
bust system. Moreover, the complete Power over Ether-
net AC disconnect system (PSE, transformers, cabling,
PD, etc.) is complex; deviating from the recommended
values of C
DET
, R
DET
and C
PSE
is discouraged. Contact the
LTC Applications department for additional support.
When choosing C
DET
and C
PSE
, carefully consider voltage
derating of the capacitors. Capacitors built around an X7R
dielectric will have about 60% of the specified capacitance
APPLICATIOU
W
U
U
Figure 15. LTC4259A Current Sense and Limits
0mA
CURRENT
R
S
= 0.5
0mV
100mA
DC DIS-
CONNECT
CUT
(I
CUT
)
LIMIT
(I
LIM
)
SHORT
CIRCUIT
EFFECT
SENSEn
VOLTAGE
50mV
200mA
100mV
300mA
150mV
400mA
200mV
500mA
250mV
600mA
300mV
CURRENT
LIMIT
PORT OFF IN t
ICUT
OR t
START
CURRENT LIMIT
IN 1
μ
s
NORMAL
OPERATION
PORT OFF IN t
DIS
4259A F15
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND
LTC4259ACGW#TR 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 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND
LTC4259ACGW#TRPBF 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 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND
LTC4259ACGW-1 制造商:Linear Technology 功能描述:QUAD IEEE 802.3AF POWER OVER ETHERNET CONTROLLER WITH AC DISCONNECT
LTC4259ACGW-1#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 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND
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