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3.4.3CapacitiveLoadDrive
3.5OptionalSignalConditioningOp-Amp(U4B)
3.6JumperSettings
EVMOperation
Itmayberequiredtodriveawiderangeofcapacitiveloads.However,undercertainconditions,allop
ampsmaybecomeunstable,dependingontheopampconfiguration,gain,andloadvalue.Thesefactors
arejustfewoftheissuesthatcanaffectopampstabilityandshouldbeconsideredduringimplementation.
Inunitygainconfiguration,theOPA627opamp(U2)performsverywellwithverylargecapacitiveloads.
Increasingthegainenhancesamplifierabilitytodriveevenmorecapacitance,andaddingaloadresistor
evenimprovesthecapacitiveloaddrivecapability.
Table6showsthejumpersettingconfigurationforacapacitiveloaddrive.
Table6.CapacitiveLoadDriveOutputJumperSettings
JumperSetting
ReferenceUnipolarBipolarFunction
JMP5OpenOpenV
REF
HisdisconnectedfromtheinvertinginputoftheoutputopampU2.
Suppliespower,V
SS
,tothenegativerailofopampU2forbipolarmode,ortiesittoAGND
JMP102-31-2
forunipolarmode.
CapacitiveloaddriveoutputofDACisroutedtopin2ofJMP6andmaybeusedasthe
JMP6OpenOpen
outputterminal.
OnehalfoftheOPA2132dualpackageopamp(U4)isusedforreferencebuffering(U4A),whiletheother
halfisunused.Thisunusedopamp(U4B)isleftforwhateveropampcircuitapplicationtheuserdesires
toimplement.The1206footprintfortheresistorsandcapacitorssurroundingtheU4Bopamparenot
populatedandaremadeavailableforeasyconfiguration.TestpointsTP5andTP6arenotinstalled,soit
isuptotheuseronhowtoconnectthe(±)inputsignalstothisopamp.Notestpointhasbeenmade
availablefortheoutputbecauseofspacerestrictions,butawirecanbesolderedtotheoutputoftheop
ampviaanunusedcomponentpadthatconnectstoit.Theopampcircuitcanbeconfiguredbypopulating
thecorrespondingcomponentstothosethatmatchthecircuitdesignwhileleavingallotherunused
componentfootprintsunpopulated.
Table7showsthefunctionofeachspecificjumpersettingoftheEVM.
Table7.JumperSettingsandFunctions
ReferenceJumperSetting
(1)
Function
ENABLEpinissethighthroughpull-upresistorR1.ENABLEcanbedrivenbyGPIO2,
J2-8.
JMP1
ENABLEpinissetlowandDACisenabled.
LDACpinissethighthroughpull-upresistorR2.LDACcanbedrivenbyGPIO0,J2-2.
JMP2
LDACpinissetlowandDACupdateisaccomplishedviasoftware.
RSTSELpinissethighthroughpull-upresistorR3.RSTSELcanbedrivenbyGPIO4,
J2-14.
JMP3
RSTSELpinissetlow.
(1)
Indicatesthecorrespondingpinsthatareshortedorclosed.
SLAU204–December2006DAC8555EVMUser'sGuide19
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