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參數(shù)資料
| 型號： | LTC4259ACGW |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 22/32頁 |
| 文件大小： | 0K |
| 描述： | IC CTRLR POE QUAD AC DISC 36SSOP |
| 標準包裝： | 32 |
| 控制器類型： | 以太網(wǎng)供電控制器（POE） |
| 接口： | I²C |
| 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） |
| 供應商設備封裝： | 36-SSOP |
| 包裝： | 管件 |
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LTC4259A
29
4259afb
APPLICATIO S I FOR ATIO
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a current loop can form. In such a loop, common mode
current flows in one port and out the other, and the choke
will not prevent this because the sum of the currents is
zero. Another way to view this interaction between the
paired ports is that the choke acts as a transformer
coupling the ports’ common modes together. In
nonpowered Ethernet, common mode current results
from nonidealities like ground loops; it is not part of
normal operation. However, Power over Ethernet sends
power and hence significant current through the ports;
common mode current is a byproduct of normal opera-
tion. As described in the Choosing External MOSFETs
section and under the Power Supplies heading below,
large transients can occur when a port’s power is turned
on or off. When a powered port is shorted (see Surge
Suppressors and Circuit Protection), a port’s common
mode current may be excessive. Sharing a common mode
choke between two ports couples start-up, disconnect
and fault transients from one port to the other. The end
result can range from momentary noncompliance with
802.3af to intermittent behavior and even to excessive
voltages that may damage circuitry (in both the PSE and
PD) connected to the ports.
Detect, AC Blocking and Transient Suppressor Diodes
During detection and classification, the LTC4259A senses
the port voltage through the detect diodes DDET in Fig-
ure 18. Excessive voltage drop across DDET will corrupt
the LTC4259A’s detect and classification results. Select a
diode for DDET that will have less than 0.7V of forward drop
at 0.4mA and less than 0.9V of forward drop at 50mA.
When the port is powered, the detect diode is reverse bi-
ased. Any leakage through the detect diode prevents the
LTC4259A from sensing all the current coupled through the
CDET capacitor. At high temperature with 70V of reverse
bias, a typical switching diode like the 1N4148 may have
more than 50
Aofleakage.Suchleakagecaninterferewith
AC disconnect because it is a large fraction of the
LTC4259A’s IACDMIN threshold. Using a low leakage detect
diode like the CMPD3003 is recommended.
The AC blocking diodes can interfere with AC disconnect
sensing if they become leaky. If the AC blocking diode (DAC
in Figure 18) begins leaking, it contributes to the Ethernet
port impedance, potentially bringing the impedance low
enough to draw IACDMIN from the DETECT pin and keep the
port powered. More likely, leakage through the AC block-
ing diode will cause shifts in the AC disconnect threshold
that are not large enough to make the PSE noncompliant.
Generally, diode leakage is caused by voltage or tempera-
ture stress. Diodes that are rated to 100V or more and can
handle dissipating at least 0.5W should be acceptable in
this application. Other component leakages can have a
similar affect on AC disconnect and even affect DC discon-
nect if the leakage becomes severe. Among components
to be wary of are the transient surge suppressors. The
devices shown in Figure 1 are rated for less than 5
A of
leakage at 58V. However there is a potential for stress
induced leakage, so healthy margins should be used when
selecting diodes for these applications.
Capacitors
Sizing of both the CDET and CPSE capacitors is critical to
proper operation of the LTC4259A’s AC disconnect sens-
ing. See the AC Disconnect section for more information.
Also, CPSE may be important to the voltage stability of a
powered port. Port voltage instability is generally not a
problem if VEE, the –48V supply, is well bypassed. For both
of these reasons be aware that many ceramic dielectrics
have dramatic DC voltage and temperature coefficients. A
0.22
F ceramic capacitor is often nowhere near 0.22F
when operating at 50VDC or 100VDC. Use 100V or higher
rated X7R capacitors for CDET and CPSE as these have re-
duced voltage dependance while also being relatively small
and inexpensive.
Power Supplies
The LTC4259A must be supplied with 3.3V (VDD) and
–48V (VEE). Poor regulation on either of these supplies
can lead to noncompliance. The IEEE requires a PSE
output voltage between 44V and 57V. When the LTC4259A
begins powering an Ethernet port, it controls the current
through the port to minimize disturbances on VEE. How-
ever, if the VEE supply is underdamped or otherwise
unstable, its voltage could go outside of the IEEE specified
limits, causing all ports in the PSE to be noncompliant.
This scenario can be even worse when a PD is unplugged
because the current can drop immediately to zero. In both
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| 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:- 標準包裝: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 供應商設備封裝: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:- 標準包裝: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 供應商設備封裝: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:- 標準包裝: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 供應商設備封裝: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:- 標準包裝: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 供應商設備封裝: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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