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| 型号： | LTC4267CGN-1#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator; Package: SSOP; No of Pins: 16; Temperature Range: 0°C to +70°C |
| 中文描述： | 1 A SWITCHING CONTROLLER, 240 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-16 |
| 文件页数： | 7/32页 |
| 文件大小： | 925K |
| 代理商： | LTC4267CGN-1#PBF |
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LTC4267-1
15
42671f
temperature exceeds the overtemperature trip point, the
current is reduced to zero and very little power is dissi-
pated in the part until it cools below the overtemperature
set point. Once the LTC4267-1 has charged up the load
capacitor and the PD is powered and running, there will
be minor residual heating due to the DC load current of
the PD owing through the internal MOSFET.
During classication, excessive heating of the LTC4267-1
can occur if the PSE violates the 75ms probing time limit.
To protect the LTC4267-1, thermal overload circuitry will
disable classication current if the die temperature exceeds
the overtemperature trip point. When the die cools down
below the trip point, classication current is reenabled.
The PD is designed to operate at a high ambient tem-
perature and with the maximum allowable supply (57V).
However, there is a limit to the size of the load capacitor
that can be charged up before the LTC4267-1 reaches the
overtemperature trip point. Hitting the overtemperature trip
point intermittently does not harm the LTC4267-1, but it
will delay the completion of capacitor charging. Capacitors
up to 200μF can be charged without a problem over the
full operating temperature range.
Switching Regulator Main Control Loop
Due to space limitations, the basics of current mode
DC/DC conversion will not be discussed here. The reader
is referred to the detail treatment in Application Note 19
or in texts such as Abraham Pressman’s Switching Power
Supply Design.
In a Power over Ethernet System, the majority of applica-
tions involve an isolated power supply design. This means
that the output power supply does not have any DC elec-
trical path to the PD interface or the switching regulator
primary. The DC isolation is achieved typically through
a transformer in the forward path and an optoisolator in
the feedback path or a third winding in the transformer.
The typical application circuit shown on the front page
of the datasheet represents an isolated design using an
optoisolator. In applications where a nonisolated topology
is desired, the LTC4267-1 features a feedback port and
an internal error amplier that can be enabled for this
specic application.
In the typical application circuit (Figure 11), the isolated
topology employs an external resistive voltage divider
to present a fraction of the output voltage to an external
error amplier. The error amplier responds by pulling
an analog current through the input LED on an optoiso-
lator. The collector of the optoisolator output presents a
corresponding current into the ITH/RUN pin via a series
diode. This method generates a feedback voltage on the
ITH/RUN pin while maintaining isolation.
The voltage on the ITH/RUN pin controls the pulse-width
modulator formed by the oscillator, current comparator,
and RS latch. Specically, the voltage at the ITH/RUN pin
sets the current comparator’s trip threshold. The current
comparator monitors the voltage across a sense resistor
in series with the source terminal of the external N-Chan-
nel MOSFET. The LTC4267-1 turns on the external power
MOSFET when the internal free-running 200kHz oscillator
sets the RS latch. It turns off the MOSFET when the cur-
rent comparator resets the latch or when 80% duty cycle
is reached, whichever happens rst. In this way, the peak
current levels through the yback transformer’s primary
and secondary are controlled by the ITH/RUN voltage.
In applications where a nonisolated topology is desirable
(Figure 11), an external resistive voltage divider can pres-
ent a fraction of the output voltage directly to the VFB pin
of the LTC4267-1. The divider must be designed so when
the output is at its desired voltage, the VFB pin voltage will
equal the 800mV onboard internal reference. The internal
error amplier responds by driving the ITH/RUN pin. The
LTC4267-1 switching regulator performs in a similar
manner as described previously.
Regulator Start-Up/Shutdown
The LTC4267-1 switching regulator has two shutdown
mechanisms to enable and disable operation: an un-
dervoltage lockout on the PVCC supply pin and a forced
shutdown whenever external circuitry drives the ITH/RUN
pin low. The LTC4267-1 switcher transitions into and out
of shutdown according to the state diagram (Figure 8).
It is important not to confuse the undervoltage lockout
of the PD interface at VPORTN with that of the switching
regulator at PVCC. They are independent functions.
APPLICATIO S I FOR ATIO
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4267CGN-1-TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator |
| LTC4267CGN-1-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator |
| LTC4267CGN-3#PBF | 功能描述:IC POE 802.3AF W/REG 16-SSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 控制器 系列:- 标准包装:2,450 系列:- 控制器类型:SPI 总线至 I²C 总线桥接 接口:I²C，串行，SPI 电源电压:2.4 V ~ 3.6 V 电流 - 电源:11mA 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:24-VFQFN 裸露焊盘 供应商设备封装:24-HVQFN（4x4） 包装:托盘 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名称:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4267CGN-3#TRPBF | 功能描述:IC POE 802.3AF INTERFACE 16SSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 控制器 系列:- 标准包装:2,450 系列:- 控制器类型:SPI 总线至 I²C 总线桥接 接口:I²C，串行，SPI 电源电压:2.4 V ~ 3.6 V 电流 - 电源:11mA 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:24-VFQFN 裸露焊盘 供应商设备封装:24-HVQFN（4x4） 包装:托盘 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名称:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4267CGNPBF | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-Ch -57V SSOP16 |
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