LTC6255 datasheet(14/24 Pages) LINER

14 / 24 page

LTC6255/LTC6256/LTC6257

625567f

thenegativesupplyto0.2Vbelowthepositivesupply,the

lowinputbiascurrentallowstheamplifierstobeusedin

applicationswithhighresistancesources.

GroundSensingandRailtoRailOutput

TheLTC6255familyhasexcellentoutputdrivecapability,

deliveringover10mAofoutputdrivecurrent.Theoutput

stageisarail-to-railtopologythatiscapableofswingingto

within30mVofeitherrail.Ifoutputswingtothenegative

railisrequired,anexternalpulldownresistortoanegative

supplycanbeadded.For5V/0Vopampsupplies,apull

downresistorof2.1kto–2Vwillallowa‘truezero’output

swing.Inthiscase,theoutputcanswingallthewayto

thebottomrailwhilemaintaining80dBofopenloopgain.

Sincetheinputscango100mVbeyondeitherrail,theop

ampcaneasilyperform‘trueground’sensing.

Themaximumoutputcurrentisafunctionoftotalsupply

voltage.Asthesupplyvoltagetotheamplifierincreases,

theoutputcurrentcapabilityalsoincreases.Attentionmust

bepaidtokeepthejunctiontemperatureoftheICbelow

150°Cwhentheoutputisincontinuousshort-circuit.The

outputoftheamplifierhasreverse-biaseddiodescon-

nectedtoeachsupply.Theoutputshouldnotbeforced

morethan0.5Vbeyondeithersupply,otherwisecurrent

willflowthroughthesediodes.

InputProtectionandOutputOverdrive

Topreventbreakdownoftheinputtransistors,theinput

stages are protected against a large differential input

voltagebytwopairsofback-to-backdiodes,D5toD8.If

thedifferentialinputvoltageexceeds1.4V,thecurrentin

thesediodesmustbelimitedtolessthan10mA.These

amplifiersarenotintendedforopenloopapplicationssuch

as comparators. When the output stage is overdriven,

internallimitingcircuitryisactivatedtoimproveoverdrive

recovery.Insomeapplications,thiscircuitrymaydrawas

muchas1mAsupplycurrent.

ESD

TheLTC6255familyhasreverse-biasedESDprotection

diodesonallinputsandoutputasshowninFigure1.

SupplyVoltageRamping

Fastrampingofthesupplyvoltagecancauseacurrent

glitchintheinternalESDprotectioncircuits.Dependingon

thesupplyinductance,thiscouldresultinasupplyvoltage

transientthatexceedsthemaximumrating.Asupplyvolt-

ageramptimeofgreaterthan1msisrecommended.

FeedbackComponents

Caremustbetakentoensurethatthepoleformedbythe

feedbackresistorsandtheparasiticcapacitanceatthe

invertinginputdoesnotdegradestability.Forexample,in

againof+2configurationwithgainandfeedbackresistors

of10k,apoorlydesignedcircuitboardlayoutwithparasitic

capacitance of 5pF (part +PC board) at the amplifier’s

invertinginputwillcausetheamplifiertooscillatedueto

apoleformedat3.2MHz.Anadditionalcapacitorof5pF

acrossthefeedbackresistorasshowninFigure2will

eliminateanyringingoroscillation.

Shutdown

ThesingleanddualversionshaveSHDNpinsthatcan

shutdowntheamplifiertolessthan7µAsupplycurrent.

TheSHDNpinvoltageneedstobewithin0.6VofV–for

theamplifiertoshutdown.Duringshutdown,theoutput

willbeinhighoutputresistancestate,whichissuitable

formultiplexerapplications.Whenleftfloating,theSHDN

pinisinternallypulleduptothepositivesupplyandthe

amplifierremainsenabled.

10k

5pF

CPAR

VOUT

VIN

625567 F02

–

LTC6255

Figure2.

ApplicAtions inForMAtion

LTC6255 Datasheet(PDF) 14 Page - Linear Technology

LTC6255 Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL