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參數(shù)資料
| 型號(hào)： | LT3837IFE#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 2/28頁 |
| 文件大?。?/td> | 247K |
| 代理商： | LT3837IFE#PBF |
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LT3837
10
3837fc
OPERATION
The LT3837 is a current mode switcher controller IC
designed specically for use in an isolated yback topology
employing synchronous rectication. The LT3837 operation
is similar to traditional current mode switchers. The major
difference is that output voltage feedback is derived via
sensing the output voltage through the transformer. This
precludes the need of an optoisolator in isolated designs
greatly improving dynamic response and reliability. The
LT3837 has a unique feedback amplier that samples a
transformer winding voltage during the yback period and
uses that voltage to control output voltage.
The internal blocks are similar to many current mode
controllers. The differences lie in the yback feedback
amplier and load compensation circuitry. The logic block
also contains circuitry to control the special dynamic
requirements of yback control.
See Application Note 19 for more information on the
basics of current mode switcher/controllers and isolated
yback converters.
Feedback Amplier—Pseudo DC Theory
For the following discussion refer to the simplied
Flyback Feedback Amplier diagram. When the primary side
MOSFET switch MP turns off, its drain voltage rises above
the VIN rail. Flyback occurs when the primary MOSFET is
off and the synchronous secondary MOSFET is on. Dur-
ing yback the voltage on nondriven transformer pins is
determined by the secondary voltage. The amplitude of this
yback pulse as seen on the third winding is given as:
V
VI
ESR R
N
FLBK
OUT
SEC
DS ON
SF
=
++
()
()
RDS(ON) = on resistance of the synchronous MOSFET MS
ISEC = transformer secondary current
ESR = impedance of secondary circuit capacitor, winding
and traces
NSF=transformereffectivesecondary-to-feedbackwinding
turns ratio (i.e., NS/NFLBK)
The yback voltage is then scaled by an external resistive
divider R1/R2 and presented at the FB pin. The feedback
amplier then compares the voltage to the internal bandgap
reference. The feedback amp is actually a transconductance
amplier whose output is connected to VC only during a
period in the yback time. An external capacitor on the VC
pin integrates the net feedback amp current to provide the
control voltage to set the current mode trip point.
The regulation voltage at the FB pin is nearly equal to the
bandgap reference VFB because of the high gain in the
overall loop. The relationship between VFLBK and VFB is
expressed as:
V
RR
R
V
FLBK
FB
= +
12
2
Combining this with the previous VFLBK expression yields
an expression for VOUT in terms of the internal reference,
programming resistors and secondary resistances:
VOUT =
+
+
RR
R
VN
I
ESR R
FB
SF
SEC
DS ON
12
2
–
()
(()
Rearranging yields the equation for R1.
RR
VI
ESR R
NV
OUT
SEC
DS ON
SF
FB
12
1
=
+
()
()()
()
–
The effect of nonzero secondary output impedance is dis-
cussed in further detail; see Load Compensation Theory.
The practical aspects of applying this equation for VOUT
are found in the Applications Information section.
Feedback Amplier Dynamic Theory
So far, this has been a pseudo-DC treatment of yback
feedback amplier operation. But the yback signal is a
pulse, not a DC level. Provision must be made to enable
the yback amplier only when the yback pulse is present.
This is accomplished by the “Enable” line in the diagram.
Timing signals are then required to enable and disable the
yback amplier. There are several timing signals which
are required for proper LT3837 operation. Please refer to
the Timing Diagram.
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| LT3844EFE#PBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| LT3844EFE#TRPBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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