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LT3845A
12
3845afa
APPLICATIONS INFORMATION
latched onto the IC control path. If the output load requires
less than this latched current level, the converter will
overdrive the output slightly during each switch cycle.
This overdrive condition is sensed internally and forces
the voltage on the VC pin to continue to drop. When the
voltage on VC drops 150mV below the 15% load level,
switching is disabled and the LT3845A shuts down most
of its internal circuitry, reducing total quiescent current
to 120A. When the converter output begins to fall, the
VC pin voltage begins to climb. When the voltage on the
VC pin climbs back to the 15% load level, the IC returns
to normal operation and switching resumes. An internal
clamp on the VC pin is set at 100mV below the switch
disable threshold, which limits the negative excursion of
the pin voltage, minimizing the converter output ripple
during Burst Mode operation.
During Burst Mode operation, VIN pin current is 20A and
VCC current is reduced to 100A. If no external drive is
provided for VCC, all VCC bias currents originate from the
VIN pin, giving a total VIN current of 120A. Burst current
can be reduced further when VCC is driven using an output
derived source, as the VCC component of VIN current is
then reduced by the converter buck ratio.
Reverse-Current Inhibit
The LT3845A contains a reverse-current inhibit feature
to maximize efficiency during light load conditions. This
mode of operation allows discontinuous operation and
pulse-skipping mode at light loads. Refer to Figure 1.
This feature is enabled with Burst Mode operation, and can
also be enabled while Burst Mode operation is disabled
by shorting the BURST_EN pin to VFB.
Whenreverse-currentinhibitisenabled,theLT3845Asense
amplifier detects inductor currents approaching zero and
disables the synchronous switch for the remainder of
the switch cycle. If the inductor current is allowed to go
negative before the synchronous switch is disabled, the
switch node could inductively kick positive with a high
dv/dt. The LT3845A prevents this by incorporating a 10mV
positive offset at the sense inputs.
Withthereverse-currentinhibitfeatureenabled,anLT3845A
converter will operate much like a nonsynchronous
converter during light loads. Reverse-current inhibit
reduces resistive losses associated with inductor ripple
currents, which improves operating efficiencies during
light-load conditions.
AnLT3845ADC/DCconverterthatisoperatinginreverse-
current inhibit mode has a minimum load requirement
of 1mA (BURST_EN = VFB). Since most applications use
output-generatedpowerfortheLT3845A,thisrequirement
is met by the bias currents of the IC, however, for
applications that do not derive power from the output,
this requirement is easily accomplished by using a 1.2k
resistor connected from VFB to ground as one of the
converter output voltage programming resistors (R1).
There are no minimum load restrictions when in Burst
Mode operation (BURST_EN < 0.5V) or continuous
conduction mode (BURST_EN > 2.5V).
Figure 1. Inductor Current vs Mode
PULSE SKIP MODE
IL
FORCED CONTINUOUS
DECREASING
LOAD
CURRENT
3845A F01
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PDF描述 |
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| LT3845EFE#TR | SWITCHING CONTROLLER, 600 kHz SWITCHING FREQ-MAX, PDSO16 |
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相關(guān)代理商/技術(shù)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(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 |
| 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(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) |
| 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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