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參數(shù)資料
| 型號(hào)： | LTC4268IDKD-1#PBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 35/46頁 |
| 文件大?。?/td> | 419K |
| 描述： | IC PD HIGH POWER W/CNTRL 32-DFN |
| 產(chǎn)品培訓(xùn)模塊： | Power over Ethernet |
| 標(biāo)準(zhǔn)包裝： | 52 |
| 類型： | 以太網(wǎng)供電開關(guān)（PoE） |
| 應(yīng)用： | 遠(yuǎn)程外設(shè)（工業(yè)控制，相機(jī)，數(shù)據(jù)訪問） |
| 內(nèi)部開關(guān)： | 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(yīng)商設(shè)備封裝： | 32-DFN（7x4）裸露焊盤 |
| 包裝： | 管件 |
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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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相關(guān)代理商/技術(shù)參數(shù) |
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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 |
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| 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(biāo)準(zhǔn)包裝:50 系列:- 類型:熱交換控制器 應(yīng)用:-48V 遠(yuǎn)程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 電流限制:可調(diào) 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(yīng)商設(shè)備封裝:10-MSOP 包裝:管件 |
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