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參數(shù)資料
| 型號： | L4974A |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Power Switching Regulator(功率開關(guān)穩(wěn)壓器) |
| 中文描述： | 電源開關(guān)穩(wěn)壓器（功率開關(guān)穩(wěn)壓器） |
| 文件頁數(shù)： | 4/22頁 |
| 文件大小： | 378K |
| 代理商： | L4974A |
The L4974A is a 3.5A monolithic stepdown swit-
chingregulatorworkingincontinuousmoderealized
inthenewBCDTechnology.Thistechnologyallows
theintegrationofisolatedverticalDMOSpowertran-
sistors plusmixed CMOS/Bipolar transistors.
Thedevicecandeliver3.5Aatanoutputvoltagead-
justablefrom 5.1V to 40V and contains diagnostic
andcontrolfunctionsthat make it particularlysuita-
blefor microprocessor basedsystems.
BLOCKDIAGRAM
The block diagram shows theDMOS powertran-
sistors and the PWM control loop. Integratedfun-
ctions include a referencevoltage trimmed to 5.1V
±
2%,softstart,undervoltagelockout,oscillatorwith
feedforward control, pulse by pulse current limit,
thermal shutdown and finally the reset and power
fail circuit. The reset and power fail circuit provides
an outputsignalfor a microprocessor indicatingthe
statusof thesystem.
Device turn on is around 11V with a typical 1V hy-
sterysis,thisthresholdporvidesacorrectvoltagefor
thedriving stage of the DMOS gateand thehyste-
rysis preventsinstabilities.
Anexternalbootstrapcapacitorchargeto12Vbyan
internalvoltagereferenceis neededto providecor-
rect gate drive to the power DMOS. The driving cir-
cuit is able to source and sink peak currents of
around0.5A to thegate of the DMOS transistor.A
typical switching time of the current in the DMOS
transistoris50ns.Due tothefastcommutationswit-
ching frequenciesup to 200kHzare possible.
ThePWM controlloop consists of a sawtoothoscil-
lator, error amplifier, comparator,latchand theout-
putstage.Anerrorsignalis producedbycomparing
theoutputvoltagewiththeprecise5.1V
±
2%onchip
reference. This error signal is then compared with
the sawtooth oscillator in order to generate frixed
frequencypulse width modulateddrive for the out-
putstage.APWMlatchisincludedtoeliminate mul-
tiple pulsing within a period even in noisy
environments.
Thegainandstability oftheloopcanbe adjustedby
an externalRCnetwork connectedto the output of
the error amplifier. A voltage feedforward control
has been addedto the oscillator, thismaintainssu-
periorlineregulation over a wide input voltageran-
ge.Closingtheloopdirectlygivesanoutputvol-tage
of 5.1V,higher voltages are obtainedbyinsertinga
voltage divider.
Atturn on,outputovercurrentsare preventedbythe
soft start function (fig. 2). The error amplifier is in-
itiallyclampedbyan externalcapacitor,Css,andal-
lowedtorise linearlyunderthechargeof aninternal
constant current source.
Outputoverloadprotection is provided bya current
limit circuit. The load current is sensed bya internal
metalresistorconnectedtoacomparator.Whenthe
load current exceedsa preset threshold, theoutput
of the comparator sets a flip flop which turns off the
powerDMOS.Thenextclockpulse,fromaninternal
40kHzoscillator,will resettheflipflopandthepower
DMOS will again conduct. This current protection
method,ensuresaconstantcurrentoutputwhenthe
systemisoverloadedorshortcircuitedandlimitsthe
switchingfrequency,inthiscondition,to40kHz.The
Reset and Power fail circuit (fig. 4), generates an
output signal when the supply voltage exceeds a
threshold programmed by an external voltage di-
vider. The reset signal, is generated with a delay
timeprogrammedbya externalcapacitoronthede-
lay pin. When the supply voltage falls below the
thresholdor the outputvoltage goes below 5V, the
resetoutputgoeslowimmediately.The resetoutput
is an open drain.
Fig. 4A shows thecase when the supplyvoltage is
higher thanthe threshold,but the outputvoltage is
not yet 5V.
Fig. 4Bshowsthecasewhenthe outputis5.1V,but
the supply voltage is not yet higher than the fixed
threshold.
The thermal protection disables circuit operation
when the junction temperature reaches about
150
°
C and has a hysterysis to prevent unstable
conditions.
CIRCUIT OPERATION
L4974A
4/22
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| L4977A | Power Switching Regulator(功率開關(guān)穩(wěn)壓器) |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L4974A | 制造商:STMicroelectronics 功能描述:IC SWITCHING REG 3.5A 4974 DIP20 |
| L4974AE | 制造商:STMicroelectronics 功能描述: |
| L4975 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:5A SWITCHING REGULATOR |
| L4975A | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 5.1 to 40V Step-Down RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| L4975A | 制造商:STMicroelectronics 功能描述:SWITCHING REG 5A 4975 MULTIWATT15 |
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