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參數(shù)資料
| 型號： | LTC4259CGW |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 4-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO36 |
| 封裝： | 0.300 INCH, PLASTIC, SSOP-36 |
| 文件頁數(shù)： | 14/32頁 |
| 文件大?。?/td> | 324K |
| 代理商： | LTC4259CGW |
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LTC4259
21
4259i
When choosing CDET and CPSE, carefully consider voltage
derating of the capacitors. Capacitors built around an X7R
dielectric will have about 60% of the specified capacitance
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. In order to produce the desired
capacitance at the operating bias, 100V X7R capacitors
should be used with the LTC4259.
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
impedance of the cable capacitance at the frequency used
for AC disconnect can be a cause for concern. Assumimg
that fOSCIN is 100Hz, the 0.1F of CPSE plus 0.05F 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. With
some methods used for AC disconnect, cable capacitance
can fool the PSE into keeping the port powered. Fortu-
nately, the LTC4259 has a solution to this problem. When
APPLICATIO S I FOR ATIO
WU
UU
Figure 16. AC Disconnect Single Channel Application Circuit
Figure 17. Simplified AC Disconnect Circuit with Impedances at 100Hz
LEVEL
SHIFT
DETECT4
AGND
DGND
OSCIN
1/4
LTC4259
–48V
GND
OUT4
ROUT4
10k
RS4
0.5
1%
DDET4
1N4148
PD
RDET4
1k
Rpd_d
≤26.25k
Cpd_d
≥0.05k
CDET4
0.22
F
100V X7R
CPSE4
0.1
F
100V X7R
4259 F16
DAC4
S1B
Q4
GATE4
SENSE4
VEE
OSCILLATOR
INPUT
CURRENT
SENSE
RDET
1k
<14k
PD
~11k
<30k
CDET
0.22
F
CPSE ≤ 0.10FCCABLE ≤ 0.05F
<30k
Cpd_d ≥ 0.05FRpd_d < 26.25k
4259 F17
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| LTC4259CGW-ES | 制造商:LINEAR_TECH 功能描述: |
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| LTC4260CGN#PBF | 功能描述:IC CTLR HOT SWAP I2C 24-SSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:119 系列:- 類型:熱交換控制器 應(yīng)用:通用型，PCI Express? 內(nèi)部開關(guān):無 電流限制:- 電源電壓:3.3V，12V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:80-TQFP 供應(yīng)商設(shè)備封裝:80-TQFP（12x12） 包裝:托盤 產(chǎn)品目錄頁面:1423 (CN2011-ZH PDF) |
| LTC4260CGN#TR | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-CH 80V 24-Pin SSOP N T/R |
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