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參數(shù)資料
| 型號： | LT3845AMPFE#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 5/26頁 |
| 文件大?。?/td> | 284K |
| 代理商： | LT3845AMPFE#PBF |
LT3845A
13
3845afa
Soft-Start
The soft-start function controls the slew rate of the power
supply output voltage during start-up. A controlled output
voltagerampminimizesoutputvoltageovershoot,reduces
inrush current from the VIN supply, and facilitates supply
sequencing. A capacitor, CSS, connected from the CSS
pin to SGND, programs the slew rate. The capacitor is
charged from an internal 2A current source producing
a ramped voltage. The capacitor voltage overrides the
internalreferencetotheerroramplifier.IftheVFBpinvoltage
exceeds the CSS pin voltage then the current threshold set
bytheDCcontrolvoltage,VC,isdecreasedandtheinductor
currentislowered.Thisinturndecreasestheoutputvoltage
slew rate allowing the CSS pin voltage ramp to catch up to
the VFB pin voltage. An internal 100mV offset is added to
the VFB pin voltage relative to the CSS pin voltage so that
at start-up the soft-start circuit will discharge the VC pin
voltage below the DC control voltage equivalent to zero
inductor current. This will reduce the input supply inrush
current. The soft-start circuit is disabled once the CSS pin
voltage has been charged to 200mV above the internal
reference of 1.231V.
During a VIN UVLO, VCC UVLO or SHDN UVLO event, the
CSS pin voltage is discharged with a 50A current source.
In normal operation the CSS pin voltage is clamped to a
diode above the VFBpinvoltage.Therefore,thevalueofthe
CSS capacitor is relevant to how long of a fault event will
retrigger a soft-start. If any of the above UVLO conditions
occur, the CSS pin voltage will be discharged with a 50A
currentsource.Thereisadiodeworthofvoltageheadroom
to ride through the fault before the CSS pin voltage enters
its active region and the soft-start function is enabled.
Also, since the CSS pin voltage is clamped to a diode above
theVFBpinvoltage,duringashortcircuittheCSSpinvoltage
is pulled low because the VFB pin voltage is low. Once
the short has been removed the VFB pin voltage starts to
recover. The soft-start circuit takes control of the output
voltage slew rate once the VFB pin voltage has exceeded
the slowly ramping CSS pin voltage, reducing the output
voltage overshoot during a short circuit recovery.
APPLICATIONS INFORMATION
Adaptive Nonoverlap (NOL) Output Stage
The FET driver output stages implement adaptive
nonoverlap control. This feature maintains a constant
dead time, preventing shoot-through switch currents,
independent of the type, size or operating conditions of
the external switch elements.
Each of the two switch drivers contains a NOL control
circuit, which monitors the output gate drive signal of the
other switch driver. The NOL control circuits interrupt the
“turn on” command to their associated switch driver until
the other switch gate is fully discharged.
Shutdown
TheLT3845ASHDNpinusesabandgapgeneratedreference
threshold of 1.35V. This precision threshold allows use of
the SHDN pin for both logic-level controlled applications
and analog monitoring applications such as power supply
sequencing.
The LT3845A operational status is primarily controlled by
a UVLO circuit on the VCC regulator pin. When the IC is
enabledviatheSHDNpin,onlytheVCCregulatorisenabled.
Switching remains disabled until the UVLO threshold is
achieved at the VCC pin, when the remainder of the IC is
enabled and switching commences.
Because an LT3845A controlled converter is a power
transfer device, a voltage that is lower than expected on
the input supply could require currents that exceed the
sourcing capabilities of that supply, causing the system
to lock up in an undervoltage state. Input supply start-up
protection can be achieved by enabling the SHDN pin
using a resistive divider from the VIN supply to ground.
Setting the divider output to 1.35V when that supply is
at an adequate voltage prevents an LT3845A converter
from drawing large currents until the input supply is able
to provide the required power. 120mV of input hysteresis
on the SHDN pin allows for almost 10% of input supply
droop before disabling the converter.
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LT3845EFE | 制造商:LINER 制造商全稱:Linear Technology 功能描述:High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency |
| LT3845EFE#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標準包裝: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® 產品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| LT3845EFE#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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) |
| LT3845EFEPBF | 制造商:Linear Technology 功能描述:60V Current-Mode Controller Adj. TSSOP16 |
| LT3845EFE-PBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency |
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