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參數(shù)資料
| 型號(hào)： | L4974 |
| 廠商： | 意法半導(dǎo)體 |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 3.5A SWITCHING REGULATOR |
| 中文描述： | 3.5A的開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 4/22頁 |
| 文件大?。?/td> | 327K |
| 代理商： | L4974 |
The L4974Ais a 3.5Amonolithic stepdownswitch-
ingregulatorworkingincontinuousmoderealizedin
the new BCD Technology. This technologyallows
theintegrationofisolatedverticalDMOSpowertran-
sistorsplusmixedCMOS/Bipolartransistors.
Thedevicecandeliver3.5Aatanoutputvoltagead-
justable from 5.1V to 40V and contains diagnostic
and control functions that make it particularly suit-
able for microprocessorbasedsystems.
BLOCKDIAGRAM
The block diagram shows theDMOSpowertran-
sistors and the PWM control loop.Integratedfunc-
tions include a reference voltage trimmed to 5.1V
±
2%,softstart,undervoltagelockout,oscillatorwith
feedforward control, pulse by pulse current limit,
thermal shutdownand finally the reset and power
failcircuit. The reset and power failcircuit provides
an outputsignalfora microprocessorindicatingthe
statusof the system.
Deviceturn on isaround11V with a typical 1Vhys-
terysis,thisthresholdporvidesa correct voltagefor
thedriving stage of the DMOS gate and the hyste-
rysis preventsinstabilities.
Anexternalbootstrapcapacitorchargeto12Vbyan
internalvoltagereferenceis neededto provide cor-
rectgatedriveto the powerDMOS.The drivingcir-
cuit is able to source and sink peak currents of
around 0.5A to the gate of the DMOS transistor. A
typical switching time of the current in the DMOS
transistor is 50ns. Due to the fast commutation
switchingfrequenciesup to 200kHzare possible.
The PWMcontrolloop consistsof a sawtoothoscil-
lator,erroramplifier, comparator,latch andthe out-
putstage.An errorsignalis producedbycomparing
theoutputvoltagewiththeprecise5.1V
±
2%onchip
reference. This error signal is then compared with
the sawtooth oscillator in order to generate frixed
frequencypulsewidth modulateddrive for the out-
put stage. A PWM latch is included to eliminate
multiple pulsing within a period even in noisy envi-
ronments.
Thegainandstabilityoftheloopcanbe adjustedby
an externalRC networkconnectedto the outputof
the error amplifier. A voltage feedforward control
has beenaddedto the oscillator,this maintainssu-
perior line regulation over a wide input voltage
range.Closing the loopdirectlygivesan outputvol-
tageof 5.1V,highervoltagesareobtainedbyinsert-
ing a voltagedivider.
Atturnon,outputovercurrentsarepreventedbythe
soft start function (fig. 2). The error amplifier is in-
itiallyclampedbyan externalcapacitor,Css,andal-
lowedto riselinearlyunderthechargeofaninternal
constantcurrentsource.
Outputoverloadprotectionis providedby a current
limitcircuit. The load currentis sensedby a internal
metalresistorconnectedtoacomparator.Whenthe
loadcurrentexceedsa presetthreshold,the output
of thecomparatorsetsa flipflop whichturns offthe
powerDMOS.Thenextclockpulse,fromaninternal
40kHzoscillator,willresettheflipflopandthepower
DMOS will again conduct. This current protection
method,ensuresaconstantcurrentoutputwhenthe
systemis overloadedorshortcircuitedandlimitsthe
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
timeprogrammedbyaexternalcapacitoronthede-
lay pin. When the supply voltage falls below the
thresholdor the outputvoltagegoes below 5V, the
resetoutputgoeslowimmediately.Theresetoutput
is an opendrain.
Fig. 4A shows the case when the supplyvoltageis
higherthan the threshold,but the outputvoltage is
not yet5V.
Fig.4Bshowsthecasewhentheoutputis5.1V,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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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L4974A | 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 |
| 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 |
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