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參數(shù)資料
| 型號(hào)： | LTC4257-1 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Power over Ethernet Interface Controller with Dual Current Limit |
| 中文描述： | 以太網(wǎng)接口控制器雙電源電流限值 |
| 文件頁數(shù)： | 16/32頁 |
| 文件大?。?/td> | 1975K |
| 代理商： | LTC4257-1 |
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LTC4267
16
4267f
important not to confuse the undervoltage lockout of the
PD interface at V
PORTN
with that of the switching regulator
at P
VCC
. They are independent functions.
prevented from reaching maximum until 1.4ms have
passed. This allows the input current of the PD to rise in a
smooth and controlled manner on start-up and stay within
the current limit requirement of the LTC4267 interface.
Adjustable Slope Compensation
The LTC4267 switching regulator injects a 5μA peak cur-
rent ramp out through its SENSE pin which can be used
for slope compensation in designs that require it. This
current ramp is approximately linear and begins at zero
current at 6% duty cycle, reaching peak current at 80%
duty cycle. Programming the slope compensation via a
series resistor is discussed in the External Interface and
Component Selection section.
EXTERNAL INTERFACE AND COMPONENT SELECTION
Input Interface Transformer
Nodes on an Ethernet network commonly interface to the
outside world via an isolation transformer (Figure 9). For
PoE devices, the isolation transformer must include a
center tap on the media (cable) side. Proper termination
is required around the transformer to provide correct
impedance matching and to avoid radiated and conducted
emissions. Transformer vendors such as Pulse, Bel Fuse,
Tyco and others (Table 3) can provide assistance with
selection of an appropriate isolation transformer and proper
termination methods. These vendors have transformers
specifically designed for use in PD applications.
Table 3. Power over Ethernet Transformer Vendors
VENDOR
Pulse Engineering
Bel Fuse Inc.
Tyco Electronics
CONTACT INFORMATION
12220 World Trade Drive
San Diego, CA 92128
Tel: 858-674-8100
FAX: 858-674-8262
http://www.pulseeng.com
206 Van Vorst Street
Jersey City, NJ 07302
Tel: 201-432-0463
FAX: 201-432-9542
http://www.belfuse.com
308 Constitution Drive
Menlo Park, CA 94025-1164
Tel: 800-227-7040
FAX: 650-361-2508
http://www.circuitprotection.com
APPLICATIOU
W
U
U
Figure 8. LTC4267 Switching Regulator
Start-Up/Shutdown State Diagram
The undervoltage lockout mechanism on P
VCC
prevents
the LTC4267 switching regulator from trying to drive the
external N-Channel MOSFET with insufficient gate-to-
source voltage. The voltage at the P
VCC
pin must exceed
V
TURNON
(nominally 8.7V with respect to PGND) at least
momentarily to enable operation. The P
VCC
voltage must
fall to V
TURNOFF
(nominally 5.7V with respect to PGND)
before the undervoltage lockout disables the switching
regulator. This wide UVLO hysteresis range supports
applications where a bias winding on the flyback trans-
former is used to increase the efficiency of the LTC4267
switching regulator.
The I
TH
/RUN can be driven below V
ITHSHDN
(nominally
0.28V with respect to PGND) to force the LTC4267 switching
regulator into shutdown. An internal 0.3μA current source
always tries to pull the I
TH
/RUN pin towards P
VCC
. When
the I
TH
/RUN pin voltage is allowed to exceed V
ITHSHDN
and
P
VCC
exceeds V
TURNON
, the LTC4267 switching regulator
begins to operate and an internal clamp immediately pulls
the I
TH
/RUN pin to about 0.7V. In operation, the I
TH
/RUN
pin voltage will vary from roughly 0.7V to 1.9V to represent
current comparator thresholds from zero to maximum.
Internal Soft-Start
An internal soft-start feature is enabled whenever the
LTC4267 switching regulator comes out of shutdown.
Specifically, the I
TH
/RUN voltage is clamped and is
LTC4267
PWM
SHUTDOWN
LTC4267
PWM
ENABLED
V
ITH
/RUN
< V
ITHSHDN
(NOMINALLY
0.28V)
V
ITH/RUN
> V
ITHSHDN
AND P
> V
(NOMINALLY 8.7V)
P
VCC
< V
TURNOFF
4267 F08
ALL VOLTAGES WITH
RESPECT TO PGND
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PDF描述 |
|---|---|
| LTC4257CDD-1 | Power over Ethernet Interface Controller with Dual Current Limit |
| LTC4267 | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LTC4267IDHC | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LTC4267IGN | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| LTC4267CGN | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
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| LTC4257CDD | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標(biāo)準(zhǔn)包裝:50 系列:- 類型:熱交換控制器 應(yīng)用:-48V 遠(yuǎn)程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 電流限制:可調(diào) 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:10-MSOP 包裝:管件 |
| LTC4257CDD#PBF | 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標(biāo)準(zhǔn)包裝:50 系列:- 類型:熱交換控制器 應(yīng)用:-48V 遠(yuǎn)程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 電流限制:可調(diào) 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:10-MSOP 包裝:管件 |
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