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参数资料
| 型号： | LTC4268CDKD-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 35/46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： | 0°C ~ 70°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
35
Converter Start-Up
The standard topology for the LTC4268-1 utilizes a third
transformer winding on the primary side that provides
both feedback information and local V
CC
power for the
LTC4268-1 (see Figure 16). This power bootstrapping
improves converter efficiency but is not inherently self-
starting. Start-up is affected with an external trickle charge
resistor and the LTC4268-1s internal V
CC
undervoltage
lockout circuit. The V
CC
undervoltage lockout has wide
hysteresis to facilitate start-up.
In operation, the trickle charge resistor R
TR
is connected
to V
IN
and supplies a small current, typically on the order
of 1mA to charge C
TR
. Initially the LTC4268-1 is off and
draws only its start-up current. When C
TR
reaches the
V
CC
turn-on threshold voltage the LTC4268-1 turns on
abruptly and draws its normal supply current.
Switching action commences and the converter begins to
deliver power to the output. Initially the output voltage is
low and the flyback voltage is also low, so C
TR
supplies
most of the LTC4268-1 current (only a fraction comes
from R
TR
.) V
CC
voltage continues to drop until after some
time, typically tens of milliseconds, the output voltage
approaches its desired value. The flyback winding then
provides the LTC4268-1 supply current and the V
CC
voltage stabilizes.
applicaTions inForMaTion
If C
TR
is undersized, V
CC
reaches the V
CC
turn-off threshold
before stabilization and the LTC4268-1 turns off. The V
CC
node then begins to charge back up via R
TR
to the turn-on
threshold, where the part again turns on. Depending upon
the circuit, this may result in either several on-off cycles
before proper operation is reached, or permanent relaxation
oscillation at the V
CC
node.
R
TR
is selected to yield a worst-case minimum charging
current greater than the maximum rated LTC4268-1 start-
up current, and a worst-case maximum charging current
less than the minimum rated LTC4268-1 supply current.
R
TR(MAX)
<
V
IN(MIN)
V
CC(ON_MAX)
I
CC(ST _MAX)
and
R
TR(MIN)
>
V
IN(MAX)
V
CC(ON_MIN)
I
CC(MIN)
Make C
TR
large enough to avoid the relaxation oscillatory
behavior described above. This is complicated to deter-
mine theoretically as it depends on the particulars of the
secondary circuit and load behavior. Empirical testing is
recommended. Note that the use of the optional soft-start
function lengthens the power-up timing and requires a
correspondingly larger value for C
TR
.
+
I
VCC
42681 F16
R
TR
C
TR
V
IN
V
IN
I
VCC
V
VCC
V
ON
THRESHOLD
0
V
PG
V
CC
LTC4268-1 PG
GND
"
"
"
Figure 16. Typical Power Bootstrapping
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4268IDKD-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power PD with Synchronous NoOpto Flyback Controller |
| LTC4268IDKD-1#PBF | 功能描述:IC PD HIGH POWER W/CNTRL 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 |
| LTC4268IDKD-1#TRPBF | 功能描述:IC PD HIGH POWER W/CNTRL 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 |
| LTC4268IDKD-1-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power PD with Synchronous NoOpto Flyback Controller |
| LTC4268IDKD-1-TR | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Power PD with Synchronous NoOpto Flyback Controller |
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