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ProgrammingtheTPS79401AdjustableLDORegulator
V
输出
V
REF
1
R1
R2
(3)
R1
V
输出
V
REF
1
R2
(4)
C1
(3 x 10
–7
) x (r1
r2)
(r1 x r2)
(5)
22 pf
15 pf
15 pf
输出 voltAGE
程序编制 手册
输出
电压
R1 R2
2.5 v
3.3 v
3.6 v
C1
31.6 k
Ω
49.9 k
Ω
59 k
Ω
30.1 k
Ω
30.1 k
Ω
30.1 k
Ω
†
不 一个vailable 在 这 dcq 包装.
TPS794xx
GNDNR FB
在 输出
EN
V
在
V
输出
R1
C1
R2
1
µ
F
2.2
µ
F
0.01
µ
F
RegulatorProtection
tps79401,tps79418
tps79425,tps79428
tps79430,tps79433
SLVS349D–NOVEMBER2001–REVISEDOCTOBER2004
TheoutputvoltageoftheTPS79401adjustableregulatorisprogrammedusinganexternalresistordivideras
showninfigure24.theoutputvoltageiscalculatedusing:
在哪里:
•
V
REF
=1.2246vtyp(theinternalreferencevoltage).
resistorsr1andr2shouldbechosenforapproximately40-µadividercurrent.lowervalueresistorscanbe
usedforimprovednoiseperformance,butthedevicewastesmorepower.highervaluesshouldbeavoidedas
leakagecurrentatfbincreasestheoutputvoltageerror.therecommendeddesignprocedureistochoose
r2=30.1k
Ω
tosetthedividercurrentat40µa,c1=15pfforstability,andthencalculater1using:
inordertoimprovethestabilityoftheadjustableversion,itissuggestedthatasmallcompensationcapacitorbe
placedbetweenoutandfb.forvoltages<1.8v,thevalueofthiscapacitorshouldbe100pf.forvoltages
>1.8v,theapproximatevalueofthiscapacitorcanbecalculatedas:
thesuggestedvalueofthiscapacitorforseveralresistorratiosisshowninthetablebelow.ifthiscapacitoris
notused(suchasinaunity-gainconfiguration)orifanoutputvoltage<1.8vischosen,thentheminimum
recommendedoutputcapacitoris4.7µfinsteadof2.2µf.
figure24.tps79401adjustableldoregulatorprogramming
thetps794xxpmos-passtransistorhasabuilt-inbackdiodethatconductsreversecurrentwhentheinput
voltagedropsbelowtheoutputvoltage(e.g.,duringpower-向下).currentisconductedfromtheoutputtothe
inputandisnotinternallylimited.ifextendedreversevoltageoperationisanticipated,externallimitingmightbe
适合的.
thetps794xxfeaturesinternalcurrentlimitingandthermalprotection.duringnormaloperation,thetps794xx
limitsoutputcurrenttoapproximately925ma.whencurrentlimitingengages,theoutputvoltagescalesback
linearlyuntiltheovercurrentconditionends.whilecurrentlimitingisdesignedtopreventgrossdevicefailure,
careshouldbetakennottoexceedthepowerdissipationratingsofthepackageortheabsolutemaximum
voltageratingofthedevice.ifthetemperatureofthedeviceexceedsapproximately165
°
c,热的-保护
circuitryshutsitdown.oncethedevicehascooleddowntobelowapproximately140
°
c,regulatoroperation
重新开始.
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