POUT
參數(shù)資料
型號(hào)： LTC4278CDKD#TRPBF
廠商： Linear Technology
文件頁數(shù)： 18/42頁
文件大?。?/td> 0K
描述： IC PD IEEE 802.3AT 25.5W 32-DFN
標(biāo)準(zhǔn)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)
LTC4278
25
4278fc
Assuming relatively fixed power supply efficiency, Eff,
power balance gives:
POUT = Eff PIN
VOUT IOUT = Eff VIN IIN
Average primary-side current is expressed in terms of
output current as follows:
IIN =K1IOUT
where:
K1=
VOUT
VIN Eff
So, the effective change in VOUT target is:
ΔVOUT =K1
RSENSE
RCMP
R1NSF ΔIOUT
thus:
ΔVOUT
ΔIOUT
=K1
RSENSE
RCMP
R1NSF
where:
K1 = dimensionless variable related to VIN, VOUT and
efficiency, as previously explained
RSENSE = external sense resistor
Nominal output impedance cancellation is obtained by
equating this expression with RS(OUT):
K1
RSENSE
RCMP
R1NSF =
ESR
+RDS(ON)
1– DC
Solving for RCMP gives:
RCMP =K1
RSENSE 1–DC
(
)
ESR
+RDS(ON)
R1NSF
Thepracticalaspectsofapplyingthisequationtodetermine
an appropriate value for the RCMP resistor are discussed
subsequently in the Applications Information section.
Transformer Design
Transformer design/specification is the most critical part
of a successful application of the LTC4278. The following
sections provide basic information about designing the
transformer and potential tradeoffs. If you need help, the
LTC Applications group is available to assist in the choice
and/or design of the transformer.
Turns Ratios
The design of the transformer starts with determining
duty cycle (DC). DC impacts the current and voltage stress
on the power switches, input and output capacitor RMS
currents and transformer utilization (size vs power). The
ideal turns ratio is:
NIIDEAL=
VOUT
VIN
1– DC
DC
Avoid extreme duty cycles, as they generally increase cur-
rent stresses. A reasonable target for duty cycle is 50%
at nominal input voltage.
For instance, if we wanted a 48V to 5V converter at 50%
DC then:
NIIDEAL=
5
48
1– 0.5
0.5
=
1
9.6
In general, better performance is obtained with a lower
turns ratio. A DC of 45.5% yields a 1:8 ratio.
APPLICATIONS INFORMATION
MP
RCMPF
50k
VIN
VFLBK
R2 LOAD
COMP I
R1
FB
VFB
Q1 Q2
RCMP
CCMP
RSENSE
SENSE+
4278 F11
Q3
–
+
A1
16
22
21
20
Figure 11. Load Compensation Diagram
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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(biāo)準(zhǔn)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(biāo)準(zhǔn)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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