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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： | 13/32页 |
| 文件大小： | 925K |
| 代理商： | LTC4267CGN-1#PBF |
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LTC4267-1
20
42671f
the cable from causing damage. However, if the VPORTN
pin is shorted to VPORTP inside the PD while the capacitor
is charged, current will ow through the parasitic body
diode of the internal MOSFET and may cause permanent
damage to the LTC4267-1.
Maintain Power Signature
In an IEEE 802.3af system, the PSE uses the maintain
power signature (MPS) to determine if a PD continues to
require power. The MPS requires the PD to periodically
draw at least 10mA and also have an AC impedance less
than 26.25k
Ω in parallel with 0.05μF. If either the DC
current is less than 10mA or the AC impedance is above
26.25k
Ω, the PSE may disconnect power. The DC current
must be less than 5mA and the AC impedance must be
above 2M
Ω to guarantee power will be removed.
Selecting Feedback Resistor Values
The regulated output voltage of the switching regulator is
determined by the resistor divider across VOUT (R1 and
R2 in Figure 11) and the error amplier reference voltage
VREF. The ratio of R2 to R1 needed to produce the desired
voltage can be calculated as:
R2 = R1 (VOUT – VREF)/VREF
In an isolated power supply application, VREF is determined
by the designer’s choice of an external error amplier.
Commercially available error ampliers or programmable
shunt regulators may include an internal reference of
1.25V or 2.5V. Since the LTC4267-1 internal reference
and error amplier are not used in an isolated design, tie
the VFB pin to PGND.
In a nonisolated power supply application, the LTC4267-1
onboard internal reference and error amplier can be
used. The resistor divider output can be tied directly to
the VFB pin. The internal reference of the LTC4267-1 is
0.8V nominal.
Choose resistance values for R1 and R2 to be as large as
possible to minimize any efciency loss due to the static
current drawn from VOUT, but just small enough so that
when VOUT is in regulation, the error caused by the nonzero
input current from the output of the resistor divider to the
error amplier pin is less than 1%.
Error Amplier and Optoisolator Considerations
In an isolated topology, the selection of the external error
amplier depends on the output voltage of the switching
regulator. Typical error ampliers include a voltage refer-
ence of either 1.25V or 2.5V. The output of the amplier
and the amplier upper supply rail are often tied together
internally. The supply rail is usually specied with a wide
upper voltage range, but it is not allowed to fall below the
reference voltage. This can be a problem in an isolated
switcher design if the amplier supply voltage is not prop-
erly managed. When the switcher load current decreases
and the output voltage rises, the error amplier responds
by pulling more current through the LED. The LED voltage
can be as large as 1.5V, and along with RLIM, reduces the
supply voltage to the error amplier. If the error amp does
not have enough headroom, the voltage drop across the
LED and RLIM may shut the amplier off momentarily,
causing a lock-up condition in the main loop. The switcher
will undershoot and not recover until the error amplier
releases its sink current. Care must be taken to select the
reference voltage and RLIM value so that the error amplier
always has enough headroom. An alternate solution that
avoids these problems is to utilize the LT1431 or LT4430
where the output of the error amplier and amplier supply
rail are brought out to separate pins.
The PD designer must also select an optoisolator such
that its bandwidth is sufciently wider than the bandwidth
of the main control loop. If this step is overlooked, the
main control loop may be difcult to stabilize. The output
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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