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參數(shù)資料
| 型號： | LTC4278CDKD#TRPBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 21/42頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC PD IEEE 802.3AT 25.5W 32-DFN |
| 標準包裝： | 2,500 |
| 控制器類型： | 供電設(shè)備接口控制器（PD） |
| 接口： | IEEE 802.3af |
| 電源電壓： | 4.5 V ~ 20 V |
| 電流 - 電源： | 6.4mA |
| 工作溫度： | 0°C ~ 70°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： | 帶卷 (TR) |
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LTC4278
28
4278fc
APPLICATIONS INFORMATION
when the peak design current is exceeded. This results
in an abrupt increase in inductor ripple current and,
consequently, output voltage ripple. Do not allow the core
to saturate! The maximum peak primary current occurs
at minimum VIN:
IPK =
PIN
VIN(MIN) DCMAX
1+ XMIN
2
now :
DCMAX =
1
1+
N VIN MIN
(
)
VOUT
=
1
1+ 1
8
41
5
=
49.4%
XMIN =
VIN(MIN) DCMAX
(
)
2
fOSC LP PIN
=
41 49.4%
(
)
2
200kHz 260H 29.5W
=
0.267
Using the example numbers leads to:
IPK =
29.5W
41 0.494
1+ 0.267
2
=1.65A
Multiple Outputs
One advantage that the flyback topology offers is that
additionaloutputvoltagescanbeobtainedsimplybyadding
windings. Designing a transformer for such a situation is
beyondthescopeofthisdocument.Formultiplewindings,
realize that the flyback winding signal is a combination of
activityonallthesecondarywindings.Thusloadregulation
is affected by each winding’s load. Take care to minimize
cross regulation effects.
Setting Feedback Resistive Divider
TheexpressionforVOUTdevelopedintheOperationsection
is rearranged to yield the following expression for the
feedback resistors:
R1=R2
VOUT +ISEC ESR+RDS(ON)
(
)
VFB NSF
1
Continuing the example, if ESR + RDS(ON) = 8mW, R2 =
3.32k, then:
R1=3.32k 5
+
5.3 0.008
1.237 1/ 3
1
= 37.28k
choose 37.4k.
It is recommended that the Thevenin impedance of the
resistive divider (R1||R2) is roughly 3k for bias current
cancellation and other reasons.
Current Sense Resistor Considerations
The external current sense resistor is used to control peak
primary switch current, which controls a number of key
converter characteristics including maximum power and
external component ratings. Use a noninductive current
sense resistor (no wire-wound resistors). Mounting the
resistordirectlyaboveanunbrokengroundplaneconnected
with wide and short traces keeps stray resistance and
inductance low.
ThedualsensepinsallowforafullKelvinconnection.Make
sure that SENSE+ and SENSE– are isolated and connect
close to the sense resistor.
Peak current occurs at 100mV of sense voltage VSENSE.So
the nominal sense resistor is VSENSE/IPK. For example, a
peakswitchcurrentof10Arequiresanominalsenseresistor
of 0.010
W Note that the instantaneous peak power in the
sense resistor is 1W, and that it is rated accordingly. The
use of parallel resistors can help achieve low resistance,
low parasitic inductance and increased power capability.
Size RSENSE using worst-case conditions, minimum LP,
VSENSE and maximum VIN. Continuing the example, let us
assume that our worst-case conditions yield an IPKof40%
above nominal, so IPK = 2.3A. If there is a 10% tolerance
on RSENSE and minimum VSENSE = 88mV, then RSENSE
110% = 88mV/2.3A and nominal RSENSE = 35mW. Round
to the nearest available lower value, 33m
W.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC4278IDKD | 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 and 12V Aux Support |
| LTC4278IDKD#PBF | 功能描述:IC PD IEEE 802.3AT 25.5W 32-DFN RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標準包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4278IDKD#TRPBF | 功能描述:IC PD IEEE 802.3AT 25.5W 32-DFN RoHS:是 類別:集成電路 (IC) >> 接口 - 控制器 系列:- 標準包裝:2,450 系列:- 控制器類型:SPI 總線至 I²C 總線橋接 接口:I²C，串行，SPI 電源電壓:2.4 V ~ 3.6 V 電流 - 電源:11mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:24-VFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:24-HVQFN（4x4） 包裝:托盤 配用:568-3511-ND - DEMO BOARD SPI TO I2C 其它名稱:935286452157SC18IS600IBSSC18IS600IBS-ND |
| LTC4278IDKDPBF | 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 and 12V Aux Support |
| LTC4278IDKDTRPBF | 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 and 12V Aux Support |
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