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參數(shù)資料
| 型號： | LT3573IMSE#TRPBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 1.85 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件頁數(shù)： | 24/26頁 |
| 文件大小： | 1182K |
| 代理商： | LT3573IMSE#TRPBF |
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LT3573
3573fc
operation
The LT3573 is a current mode switching regulator IC
designed specifically for the isolated flyback topology.
The special problem normally encountered in such cir-
cuits is that information relating to the output voltage on
the isolated secondary side of the transformer must be
communicated to the primary side in order to maintain
regulation. Historically, this has been done with opto-
isolators or extra transformer windings. Opto-isolator
circuits waste output power and the extra components
increase the cost and physical size of the power supply.
Opto-isolators can also exhibit trouble due to limited
dynamic response, nonlinearity, unit-to-unit variation
and aging over life. Circuits employing extra transformer
windings also exhibit deficiencies. Using an extra wind-
ing adds to the transformer’s physical size and cost, and
dynamic response is often mediocre.
The LT3573 derives its information about the isolated
output voltage by examining the primary-side flyback
pulse waveform. In this manner, no opto-isolator nor extra
transformer winding is required for regulation. The output
voltageiseasilyprogrammedwithtworesistors.Sincethis
IC operates in boundary control mode, the output voltage
is calculated from the switch pin when the secondary cur-
rent is almost zero. This method improves load regulation
without external resistors and capacitors.
The Block Diagram shows an overall view of the system.
Many of the blocks are similar to those found in traditional
switching regulators including: internal bias regulator,
oscillator, logic, current amplifier and comparator, driver,
and output switch. The novel sections include a special
flyback error amplifier and a temperature compensation
circuit. In addition, the logic system contains additional
logic for boundary mode operation, and the sampling
error amplifier.
The LT3573 features a boundary mode control method,
where the part operates at the boundary between continu-
ousconductionmodeanddiscontinuousconductionmode.
TheVCpincontrolsthecurrentleveljustasitdoesinnormal
current mode operation, but instead of turning the switch
on at the start of the oscillator period, the part detects
when the secondary side winding current is zero.
Boundary Mode Operation
Boundary mode is a variable frequency, current-mode
switching scheme. The switch turns on and the inductor
currentincreasesuntilaVCpincontrolledcurrentlimit.The
voltage on the SW pin rises to the output voltage divided
by the secondary-to-primary transformer turns ratio plus
the input voltage. When the secondary current through
the diode falls to zero, the SW pin voltage falls below VIN.
A discontinuous conduction mode (DCM) comparator
detects this event and turns the switch back on.
Boundary mode returns the secondary current to zero
every cycle, so the parasitic resistive voltage drops do not
cause load regulation errors. Boundary mode also allows
the use of a smaller transformer compared to continuous
conduction mode and no subharmonic oscillation.
At low output currents the LT3573 delays turning on the
switch, and thus operates in discontinuous mode. Unlike
a traditional flyback converter, the switch has to turn on
to update the output voltage information. Below 0.6V on
the VC pin, the current comparator level decreases to
its minimum value, and the internal oscillator frequency
decreases in frequency. With the decrease of the internal
oscillator, the part starts to operate in DCM. The output
current is able to decrease while still allowing a minimum
switch off-time for the error amp sampling circuitry. The
typical minimum internal oscillator frequency with VC
equal to 0V is 40kHz.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LT3581EDE#PBF | SWITCHING REGULATOR, PDSO14 |
| LT3581EDE#TRPBF | SWITCHING REGULATOR, PDSO14 |
| LT3581EMSE#PBF | SWITCHING REGULATOR, PDSO16 |
| LT3581EMSE#TRPBF | SWITCHING REGULATOR, PDSO16 |
| LT3581IDE#TRPBF | SWITCHING REGULATOR, PDSO14 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT3574 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
| LT3574EMS | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
| LT3574EMS#PBF | 功能描述:IC REG FLYBK ISO ADJ .65A 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2 |
| LT3574EMS#TRPBF | 功能描述:IC REG FLYBK ISO ADJ .65A 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤 |
| LT3574EMSPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
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