Operating Information
Output Voltage Adjust (Vadj
)
Input And Output Impedance
Theꢀoutputꢀvoltageꢀcanꢀbeꢀsetꢀbyꢀmeansꢀofꢀanꢀexternalꢀ
resistor,ꢀconnectedꢀtoꢀtheꢀVadjꢀpin.ꢀNominalꢀoutputꢀvoltageꢀ
0.75ꢀVꢀisꢀsetꢀbyꢀleavingꢀtheꢀVadjꢀpinꢀopen.ꢀAdjustmentꢀcanꢀ
onlyꢀbeꢀmadeꢀtoꢀincreaseꢀtheꢀoutputꢀvoltageꢀsetting.
Theꢀimpedanceꢀofꢀbothꢀtheꢀpowerꢀsourceꢀandꢀtheꢀloadꢀwillꢀ
interactꢀwithꢀtheꢀimpedanceꢀofꢀtheꢀDC/DCꢀregulator.ꢀItꢀisꢀ
mostꢀimportantꢀtoꢀhaveꢀaꢀlowꢀcharacteristicꢀimpedance,ꢀ
bothꢀatꢀtheꢀinputꢀandꢀoutput,ꢀasꢀtheꢀregulatorsꢀhaveꢀaꢀlowꢀ
energyꢀstorageꢀcapability.ꢀUseꢀcapacitorsꢀacrossꢀtheꢀinputꢀifꢀ
theꢀsourceꢀinductanceꢀisꢀgreaterꢀthanꢀ4.7ꢀµH.ꢀSuitableꢀinputꢀ
capacitorsꢀareꢀ22ꢀµFꢀ-ꢀ220ꢀµFꢀlowꢀESRꢀceramics.ꢀ
Toꢀincrease:ꢀꢀ
Connectꢀaꢀresistorꢀbetweenꢀ(Vadj)ꢀandꢀ(Gnd).ꢀTheꢀoutputꢀ
voltageꢀincreasesꢀwithꢀdecreasingꢀresistorꢀvalueꢀasꢀshownꢀ
inꢀtheꢀtableꢀbelow.ꢀNoteꢀthatꢀtheꢀmaximumꢀoutputꢀvoltageꢀ
3.63ꢀVꢀmayꢀnotꢀbeꢀexceeded.
Minimum Required External Capacitors
Externalꢀinputꢀcapacitorsꢀareꢀrequiredꢀtoꢀincreaseꢀtheꢀ
lifetimeꢀofꢀtheꢀinternalꢀcapacitorsꢀandꢀtoꢀfurtherꢀreduceꢀtheꢀ
inputꢀripple.ꢀAꢀminimumꢀofꢀ2x22ꢀµFꢀexternalꢀinputꢀcapaci-
tanceꢀwithꢀlowꢀESRꢀshouldꢀbeꢀadded.
Rextꢀupꢀ(kohm)ꢀ=ꢀ(21.007ꢀ/ꢀ(VOꢀ-ꢀ0.75225))ꢀ-ꢀ5.1ꢀ
OutputꢀVoltageꢀ(V)
Resistorꢀ(ohm)
Open
Aꢀminimumꢀofꢀ150ꢀµFꢀexternalꢀoutputꢀcapacitance,ꢀlowꢀESR,ꢀ
shouldꢀbeꢀaddedꢀforꢀtheꢀconverterꢀtoꢀoperateꢀproperlyꢀatꢀfullꢀ
load.ꢀꢀꢀꢀꢀ
0.75
1.0
1.2
1.5
1.8
2.5
3.3
79.691ꢀk
41.817ꢀk
22.990ꢀk
14.949ꢀk
6.919ꢀk
Maximum Capacitive Load
Whenꢀpoweringꢀloadsꢀwithꢀsignificantꢀdynamicꢀcurrentꢀ
requirements,ꢀtheꢀvoltageꢀregulationꢀatꢀtheꢀloadꢀcanꢀbe
improvedꢀbyꢀadditionꢀofꢀdecouplingꢀcapacitanceꢀatꢀtheꢀload.ꢀ
TheꢀmostꢀeffectiveꢀtechniqueꢀisꢀtoꢀlocateꢀlowꢀESRꢀceramicꢀ
capacitorsꢀasꢀcloseꢀtoꢀtheꢀloadꢀasꢀpossible,ꢀusingꢀseveralꢀ
capacitorsꢀtoꢀlowerꢀtheꢀtotalꢀESR.ꢀTheseꢀceramicꢀcapacitorsꢀ
willꢀhandleꢀshortꢀdurationꢀhigh-frequencyꢀcomponentsꢀ
ofꢀdynamicꢀloadꢀchanges.ꢀInꢀaddition,ꢀhigherꢀvaluesꢀofꢀ
capacitorsꢀ(electrolyticꢀcapacitors)ꢀshouldꢀbeꢀusedꢀtoꢀhandleꢀ
theꢀmid-frequencyꢀcomponents.ꢀItꢀisꢀequallyꢀimportantꢀ
toꢀuseꢀgoodꢀdesignꢀpracticeꢀwhenꢀconfiguringꢀtheꢀDCꢀ
distributionꢀsystem.
3.145ꢀk
+Out
Sense
LowꢀresistanceꢀandꢀlowꢀinductanceꢀPCBꢀlayoutsꢀandꢀ
cablingꢀshouldꢀbeꢀused.ꢀRememberꢀthatꢀwhenꢀusingꢀremoteꢀ
sensing,ꢀallꢀresistanceꢀ(includingꢀtheꢀESR),ꢀinductanceꢀandꢀ
capacitanceꢀofꢀtheꢀdistributionꢀsystemꢀisꢀwithinꢀtheꢀfeedbackꢀ
loopꢀofꢀtheꢀregulator.ꢀThisꢀcanꢀaffectꢀonꢀtheꢀregulatorsꢀ
compensationꢀandꢀtheꢀresultingꢀstabilityꢀandꢀdynamicꢀ
responseꢀperformance.
Load
V
adj
R
adj
GND
Increase
VeryꢀlowꢀESRꢀandꢀhighꢀcapacitanceꢀmustꢀbeꢀusedꢀwithꢀ
care.ꢀAꢀ“ruleꢀofꢀthumb”ꢀisꢀthatꢀtheꢀtotalꢀcapacitanceꢀmustꢀ
neverꢀexceedꢀtypicallyꢀ500-700ꢀµFꢀifꢀonlyꢀlowꢀESRꢀ(<ꢀ2ꢀmΩ)ꢀ
ceramicꢀcapacitorsꢀareꢀused.ꢀIfꢀmoreꢀcapacitanceꢀisꢀneeded,ꢀ
aꢀcombinationꢀofꢀlowꢀESRꢀtypeꢀandꢀelectrolyticꢀcapacitorsꢀ
shouldꢀbeꢀused,ꢀotherwiseꢀtheꢀstabilityꢀwillꢀbeꢀaffected.
Circuitꢀconfigurationꢀforꢀoutputꢀvoltageꢀadjust
Current Limit Protection
TheꢀPMBꢀ4000ꢀSeriesꢀDC/DCꢀregulatorsꢀincludeꢀcurrentꢀ
limitingꢀcircuitryꢀthatꢀallowsꢀthemꢀtoꢀwithstandꢀcontinuousꢀ
overloadsꢀorꢀshortꢀcircuitꢀconditionsꢀonꢀtheꢀoutput.ꢀTheꢀcur-
rentꢀlimitꢀisꢀofꢀhick-upꢀmodeꢀtype.
Theꢀregulatorꢀwillꢀresumeꢀnormalꢀoperationꢀafterꢀremovalꢀ
ofꢀtheꢀoverload.ꢀTheꢀloadꢀdistributionꢀsystemꢀshouldꢀbeꢀ
designedꢀtoꢀcarryꢀtheꢀmaximumꢀoutputꢀshortꢀcircuitꢀcurrentꢀ
specified.
TheꢀPMBꢀ4000ꢀseriesꢀregulatorꢀcanꢀacceptꢀupꢀtoꢀ8ꢀmFꢀofꢀ
capacitiveꢀloadꢀonꢀtheꢀoutputꢀatꢀfullꢀload.ꢀThisꢀgivesꢀ<500ꢀ
µF/AꢀofꢀIO.ꢀWhenꢀusingꢀthatꢀlargeꢀcapacitanceꢀitꢀisꢀimportantꢀ
toꢀconsiderꢀtheꢀselectionꢀofꢀoutputꢀcapacitors;ꢀtheꢀresultingꢀ
behaviorꢀisꢀaꢀcombinationꢀofꢀtheꢀamountꢀofꢀcapacitanceꢀandꢀ
ESR.
ꢀꢃ
ꢀꢀꢀꢀꢀꢀEN/LZTꢀ146ꢀ049ꢀR4Aꢀ©EricssonꢀPowerꢀModules,ꢀMarchꢀ2007
PMBꢀ4518TꢀWPꢀDatasheet
ERICSSON [ ERICSSON ]
