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參數資料
| 型號： | LTC4268IDKD-1#PBF |
| 廠商： | Linear Technology |
| 文件頁數： | 36/46頁 |
| 文件大小： | 419K |
| 描述： | IC PD HIGH POWER W/CNTRL 32-DFN |
| 產品培訓模塊： | Power over Ethernet |
| 標準包裝： | 52 |
| 類型： | 以太網供電開關（PoE） |
| 應用： | 遠程外設（工業控制，相機，數據訪問） |
| 內部開關： | 是 |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 32-WFDFN 裸露焊盤 |
| 供應商設備封裝： | 32-DFN（7x4）裸露焊盤 |
| 包裝： | 管件 |
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LTC4268-1
36
42681fc
applicaTions inForMaTion
The LTC4268-1 has an internal clamp on V
CC
of approxi-
mately 20V. This provides some protection for the part
in the event that the switcher is off (UVLO low) and the
V
CC
node is pulled high. If R
TR
is sized correctly the part
should never attain this clamp voltage.
Control Loop Compensation
Loop frequency compensation is performed by connect-
ing a capacitor network from the output of the feedback
amplifier (V
CMP
pin) to ground as shown in Figure 17.
Because of the sampling behavior of the feedback amplifier,
compensation is different from traditional current mode
controllers. Normally only C
VCMP
is required. R
VCMP
can
be used to add a zero but the phase margin improve-
ment traditionally offered by this extra resistor is usually
already accomplished by the nonzero secondary circuit
impedance. C
VCMP2
can be used to add an additional high
frequency pole and is usually sized at 0.1 times C
VCMP
.
In further contrast to traditional current mode switchers,
V
CMP
pin ripple is generally not an issue with the LTC4268-1.
The dynamic nature of the clamped feedback amplifier
forms an effective track/hold type response, whereby the
V
CMP
voltage changes during the flyback pulse, but is then
held during the subsequent switch on portion of the
next cycle. This action naturally holds the V
CMP
voltage
stable during the current comparator sense action (current
mode switching).
Application Note 19 provides a method for empirically
tweaking frequency compensation. Basically it involves
introducing a load current step and monitoring the
response.
Slope Compensation
The LTC4268-1 incorporates current slope compensation.
Slope compensation is required to ensure current loop
stability when the DC is greater than 50%. In some switching
regulators, slope compensation reduces the maximum peak
current at higher duty cycles. The LTC4268-1 eliminates
this problem by having circuitry that compensates for
the slope compensation so that maximum current sense
voltage is constant across all duty cycles.
Minimum Load Considerations
At light loads, the LTC4268-1 derived regulator goes into
forced continuous conduction mode. The primary side
switch always turns on for a short time as set by the
t
ON(MIN)
resistor. If this produces more power than the
load requires, power will flow back into the primary during
the off period when the synchronization switch is on.
This does not produce any inherently adverse problems,
although light load efficiency is reduced.
Maximum Load Considerations
The current mode control uses the V
CMP
node voltage and
amplified sense resistor voltage as inputs to the current
comparator. When the amplified sense voltage exceeds the
V
CMP
node voltage, the primary side switch is turned off.
In normal use, the peak switch current increases while
FB is below the internal reference. This continues until
V
CMP
reaches its 2.56V clamp. At clamp, the primary side
MOSFET will turn off at the rated 100mV V
SENSE
level. This
repeats on the next cycle. It is possible for the peak primary
switch currents as referred across R
SENSE
to exceed the
17
R
VCMP
V
CMP
C
VCMP
42681 F17
C
VCMP2
Figure 17. V
CMP
Compensation Network
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相關代理商/技術參數 |
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|---|---|
| LTC4268IDKD-1-TR | 制造商:LINER 制造商全稱:Linear Technology 功能描述:High Power PD with Synchronous NoOpto Flyback Controller |
| LTC4268IDKD-1-TRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:High Power PD with Synchronous NoOpto Flyback Controller |
| LTC4269-1 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:IEEE 802.3at PD with Synchronous No-Opto Flyback Controller |
| LTC4269-2 | 制造商:LINER 制造商全稱: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 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統，AdvancedTCA ? 系統，高可用性 內部開關:無 電流限制:可調 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） 供應商設備封裝:10-MSOP 包裝:管件 |
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