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参数资料
| 型号： | LTC4268IDKD-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 37/46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
37
applicaTions inForMaTion
max 100mV rating because of the minimum switch on
time blanking. If the voltage on V
SENSE
exceeds 205mV
after the minimum turn-on time, the SFST capacitor is
discharged, causing the discharge of the V
CMP
capacitor.
This then reduces the peak current on the next cycle and
will reduce overall stress in the primary switch.
Short-Circuit Conditions
Loss of current limit is possible under certain conditions
such as an output short circuit. If the duty cycle exhibited
by the minimum on time is greater than the ratio of
secondary winding voltage (referred-to-primary) divided
by input voltage, then peak current is not controlled at
the nominal value. It ratchets up cycle-by-cycle to some
higher level. Expressed mathematically, the requirement
to maintain short-circuit control is
DC
MIN
= t
ON(MIN)
f
OSC
<
I
SC
R
SEC
+R
DS(ON)
(
)
V
IN
N
SP
where:
t
ON(MIN)
is the primary side switch minimum on-time
I
SC
is the short-circuit output current
N
SP
is the secondary-to-primary turns ratio (N
SEC
/N
PRI
)
(Other variables as previously defined)
Trouble is typically encountered only in applications with a
relatively high product of input voltage times secondary to
primary turns ratio and/or a relatively long minimum switch
on time. Additionally, several real world effects such as
transformer leakage inductance, AC winding losses, and
output switch voltage drop combine to make this simple
theoretical calculation a conservative estimate. Prudent
design evaluates the switcher for short-circuit protection
and adds any additional circuitry to prevent destruction
for these losses.
Output Voltage Error Sources
The LTC4268-1s feedback sensing introduces additional
minor sources of errors. The following is a summary list.
" The internal bandgap voltage reference sets the reference
voltage for the feedback amplifier. The specifications
detail its variation.
" The external feedback resistive divider ratio directly
affects regulated voltage. Use 1% components.
" Leakage inductance on the transformer secondary
reduces the effective secondary-to-feedback winding
turns ratio (NS/NF) from its ideal value. This increases
the output voltage target by a similar percentage. Since
secondary leakage inductance is constant from part to
part (within a tolerance) adjust the feedback resistor
ratio to compensate.
" The transformer secondary current flows through the
impedances of the winding resistance, synchronous
MOSFET R
DS(ON)
and output capacitor ESR. The DC
equivalent current for these errors is higher than the
load current because conduction occurs only during
the converters off time. So divide the load current
by (1 DC).
If the output load current is relatively constant, the feedback
resistive divider is used to compensate for these losses.
Otherwise, use the LTC4268-1 load compensation circuitry.
(See Load Compensation.) If multiple output windings are
used, the flyback winding will have a signal that represents
an amalgamation of all these windings impedances. Take
care that you examine worst-case loading conditions when
tweaking the voltages.
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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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