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參數(shù)資料
| 型號： | 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 |
| 文件頁數(shù)： | 21/32頁 |
| 文件大?。?/td> | 326K |
| 代理商： | LTC4259ACGW |
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LTC4259A
21
4259Af
at their rated voltage. Operated at half their rated voltage,
X7R capacitors exhibit more than 80% of their specified
capacitance. With other ceramic dielectrics commonly
used in 50V and 100V chip capacitors, capacitance falls
much more dramatically with voltage. At their rated volt-
age, Y5V or Z5U capacitors exhibit less than 30% of their
zero-bias capacitance. Ceramic capacitors can also have
significantly less capacitance at elevated temperatures. In
order to produce the desired capacitance at the operating
bias, 100V or 250V X7R capacitors should be used with
the LTC4259A.
As illustrated in Figure 17, the Power over Ethernet con-
nection between the PSE and PD includes a large amount
of capacitance. Cable capacitance is particularly troubling
because CAT-3 and CAT-5 pair-to-pair capacitance is not
tightly specified by the IEEE 802.3 standard or well con-
trolled by cable manufacturers. Considering that patch
panels, additional connectors, old wiring, etc. are likely to
be placed between the PSE and PD, pair-to-pair capaci-
tance is a pretty nebulous quantity. Consequently, the
cable’s contribution to the port impedance (at the fre-
quency used for AC disconnect) can be a concern.
Assumimg that f
OSCIN
is 100Hz, the 0.1
μ
F of C
PSE
plus
0.05
μ
F of cable capacitance gives a port impedance of 10k
at 100Hz. The PD AC signature resistance is about 25k.
Connecting a PD with the maximum allowed resistance of
26.25k brings the connection impedance to about 8k. The
presence of a PD only makes a 20% reduction in the port
impedance requiring the AC disconnect circuitry to be
quite sensitive. When the OSCIN pin is driven with a sine
wave, the LTC4259A is able to distinguish between capaci-
tive impedance and resistive impedance on the Power over
Ethernet connection. AC disconnect is reliable for cable
capacitance up to about 0.2
μ
F, nearly an order of magni-
tude greater than worst case for a long CAT-3 or CAT-5
cable.
APPLICATIOU
W
U
U
Figure 16. AC Disconnect Single Port Application Circuit (Port 4 Shown)
Figure 17. Simplified AC Disconnect Circuit with Impedances at 100Hz
LEVEL
SHIFT
DETECT4
AGND
DGND
OSCIN
1/4
LTC4259A
–48V
GND
OUT4
R
OUT4
10k
R
S4
0.5
1%
D
CMPD3003
PD
R
DET4
1k
Rpd_d
≤
26.25k
Cpd_d
≥
0.05
μ
F
C
0.47
μ
F
100V X7R
C
PSE4
0.1
F
100V X7R
4259A F16
D
S1B
Q4
GATE4
SENSE4
V
EE
OSCILLATOR
INPUT
CURRENT
SENSE
R
DET
1k
C
0.47
μ
F
Z
LINK
< 14k
Z
CABLE
< 32k
PD
~16k
~7k
Z
PD
< 14k
C
0.10
μ
F
C
CABLE
≤
0.05
μ
F
<32k
C
pd_d
≥
0.05
μ
F
R
pd_d
< 26.25k
4259A F17
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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(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(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(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(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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