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参数资料
| 型号： | LTC4268IDKD-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 25/46页 |
| 文件大小： | 419K |
| 描述： | IC PD HIGH POWER W/CNTRL 32-DFN |
| 标准包装： | 2,500 |
| 类型： | 以太网供电开关（PoE） |
| 应用： | 远程外设（工业控制，相机，数据访问） |
| 内部开关： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFDFN 裸露焊盘 |
| 供应商设备封装： | 32-DFN（7x4）裸露焊盘 |
| 包装： | 带卷 (TR) |
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42681fc
LTC4268-1
25
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 in parallel with 0.05礔. If either the DC current
is less than 10mA or the AC impedance is above 26.25k,
the PSE may disconnect power. The DC current must be
less than 5mA and the AC impedance must be above 2M
to guarantee power will be removed. The PD application
circuits shown in this data sheet present the required AC
impedance necessary to maintain power.
IEEE 802.3at Interoperability
In anticipation of the IEEE 802.3at standard release, the
LTC4268-1 can be combined with a simple external circuit
to be fully interoperable with an IEEE 802.3at-compliant
PSE. For more information, please contact Linear Technol-
ogys Application Engineering.
SWITCHING REGULATOR OVERVIEW
The LTC4268-1 includes a current mode converter designed
specifically for use in an isolated flyback topology employing
synchronous rectification. The LTC4268-1 operation is
similar to traditional current mode switchers. The major
difference is that output voltage feedback is derived via
sensing the output voltage through
the transformer. This
precludes the need of an opto-isolator in isolated designs
greatly improving dynamic response and reliability. The
LTC4268-1 has a unique feedback amplifier that samples a
transformer winding voltage during the flyback period and
uses that voltage to control output voltage. The internal
blocks are similar to many current mode controllers.
The differences lie in the feedback amplifier and load
compensation circuitry. The logic block also contains
circuitry to control the special dynamic requirements of
flyback control. For more information on the basics of
current mode switcher/controllers and isolated flyback
converters see Application Note 19.
Feedback AmplifierPseudo DC Theory
For the following discussion refer to the simplified Flyback
Amplifier diagram(Figure 12). When the primary side
MOSFET switch MP turns off, its drain voltage rises above
the V
PORTP
rail. Flyback occurs when the primary MOSFET
is off and the synchronous secondary MOSFET is on.
During flyback the voltage on nondriven transformer pins
is determined by the secondary voltage. The amplitude of
this flyback pulse as seen on the third winding is given as:
V
FLBK
=
V
OUT
+I
SEC
ESR +R
DS(ON)
(
)
N
SF
R
DS(ON)
= on resistance of the synchronous MOSFET MS
I
SEC
= transformer secondary current
ESR = impedance of secondary circuit capacitor, winding
and traces
N
SF
= transformer effective secondary-to-flyback winding
turns ratio (i.e., N
S
/N
FLBK
)
applicaTions inForMaTion
+
V
FB
1.237V
ENABLE
COLLAPSE
DETECT
1V
LTC4268-1 FEEDBACK AMP
FB
R1
R2
16
17
V
CMP
V
IN
PRIMARY
FLYBACK
SECONDARY
"
"
"
MP
T1
V
FLBK
MS
C
VC
42681 F12
C
OUT
ISOLATED
OUTPUT
+
S
R
Q
Figure 12. LTC4268-1 Switching Regulator Feedback Amplifier
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4269-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at PD with Synchronous No-Opto Flyback Controller |
| LTC4269-2 | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at High Power PD and Synchronous Forward Controller with AUX Support |
| LTC4269CDKD-1#PBF | 功能描述:IC PD/OPTO FLYBACK CTRLR 32-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4269CDKD-1#TRPBF | 功能描述:IC PD/OPTO FLYBACK CTRLR 32-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:100 系列:- 类型:热插拔开关 应用:通用 内部开关:是 电流限制:可调 电源电压:9 V ~ 13.2 V 工作温度:-40°C ~ 150°C 安装类型:表面贴装 封装/外壳:10-WFDFN 裸露焊盘 供应商设备封装:10-TDFN-EP（3x3） 包装:管件 |
| LTC4269CDKD-1-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at PD with Synchronous No-Opto Flyback Controller |
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